webauthn_rp

register.rs (89418B)

---

 #[cfg(test)]
 mod tests;
 use super::{
     super::{
         DynamicState, Metadata, RegisteredCredential, StaticState,
         response::{
             AuthenticatorAttachment,
             register::{
                 Attestation, AttestationFormat, AuthenticatorExtensionOutput,
                 ClientExtensionsOutputs, CredentialProtectionPolicy, HmacSecret, Registration,
                 UncompressedPubKey,
                 error::{ExtensionErr, RegCeremonyErr},
             },
         },
     },
     Ceremony, Challenge, CredentialMediationRequirement, ExtensionInfo, ExtensionReq, FIVE_MINUTES,
     Hints, Origin, PrfInput, PublicKeyCredentialDescriptor, RpId, SentChallenge, TimedCeremony,
     UserVerificationRequirement,
     register::error::CreationOptionsErr,
 };
 #[cfg(doc)]
 use crate::{
     request::{
         AsciiDomain, AsciiDomainStatic, DomainOrigin, Url,
         auth::{AuthenticationVerificationOptions, PublicKeyCredentialRequestOptions},
     },
     response::{AuthTransports, AuthenticatorTransport, Backup, CollectedClientData, Flag},
 };
 use core::{
     borrow::Borrow,
     cmp::Ordering,
     fmt::{self, Display, Formatter},
     hash::{Hash, Hasher},
     mem,
     num::{NonZeroU32, NonZeroU64},
     time::Duration,
 };
 #[cfg(any(doc, not(feature = "serializable_server_state")))]
 use std::time::Instant;
 #[cfg(any(doc, feature = "serializable_server_state"))]
 use std::time::SystemTime;
 /// Contains functionality to (de)serialize data to a data store.
 #[cfg(feature = "bin")]
 pub mod bin;
 /// Contains functionality that needs to be accessible when `bin` or `serde` are not enabled.
 #[cfg(feature = "custom")]
 mod custom;
 /// Contains error types.
 pub mod error;
 /// Contains functionality to (de)serialize data to a client.
 #[cfg(feature = "serde")]
 pub mod ser;
 /// Contains functionality to (de)serialize [`RegistrationServerState`] to a data store.
 #[cfg(feature = "serializable_server_state")]
 pub mod ser_server_state;
 /// Backup requirements for the credential.
 #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
 pub enum BackupReq {
     /// No requirements (i.e., any [`Backup`] is allowed).
     #[default]
     None,
     /// Credential must not be eligible for backup.
     NotEligible,
     /// Credential must be eligible for backup.
     ///
     /// Note the existence of a backup is ignored. If a backup must exist, then use [`Self::Exists`]; if a
     /// backup must not exist, then use [`Self::EligibleNotExists`].
     Eligible,
     /// Credential must be eligible for backup, but a backup must not exist.
     EligibleNotExists,
     /// Credential must be backed up.
     Exists,
 }
 /// Used by [`Extension::cred_protect`] to enforce the [`CredentialProtectionPolicy`] sent by the client via
 /// [`Registration`].
 #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
 pub enum CredProtect {
     /// No `credProtect` request.
     #[default]
     None,
     /// Request
     /// [`userVerificationOptional`](https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#userverificationoptional)
     /// but allow any.
     ///
     /// The `bool` corresponds to
     /// [`enforceCredentialProtectionPolicy`](https://fidoalliance.org/specs/fido-v2.2-ps-20250228/fido-client-to-authenticator-protocol-v2.2-ps-20250228.html#dom-authenticationextensionsclientinputs-enforcecredentialprotectionpolicy).
     UserVerificationOptional(bool, ExtensionInfo),
     /// Request
     /// [`userVerificationOptionalWithCredentialIDList`](https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#userverificationoptionalwithcredentialidlist);
     /// and when enforcing the value, disallow [`CredentialProtectionPolicy::UserVerificationOptional`].
     ///
     /// The `bool` corresponds to
     /// [`enforceCredentialProtectionPolicy`](https://fidoalliance.org/specs/fido-v2.2-ps-20250228/fido-client-to-authenticator-protocol-v2.2-ps-20250228.html#dom-authenticationextensionsclientinputs-enforcecredentialprotectionpolicy).
     UserVerificationOptionalWithCredentialIdList(bool, ExtensionInfo),
     /// Request
     /// [`userVerificationRequired`](https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#userverificationrequired);
     /// and when enforcing the value, only allow [`CredentialProtectionPolicy::UserVerificationRequired`].
     ///
     /// The `bool` corresponds to
     /// [`enforceCredentialProtectionPolicy`](https://fidoalliance.org/specs/fido-v2.2-ps-20250228/fido-client-to-authenticator-protocol-v2.2-ps-20250228.html#dom-authenticationextensionsclientinputs-enforcecredentialprotectionpolicy).
     UserVerificationRequired(bool, ExtensionInfo),
 }
 impl CredProtect {
     /// Validates `other` is allowed based on `self`.
     ///
     /// # Errors
     ///
     /// Errors iff other is a less "secure" policy than `self` when enforcing the value or other does not exist
     /// despite requiring a value to be sent back.
     ///
     /// Note a missing response is OK when enforcing a value.
     const fn validate(self, other: CredentialProtectionPolicy) -> Result<(), ExtensionErr> {
         match self {
             Self::None => Ok(()),
             Self::UserVerificationOptional(_, info) => {
                 if matches!(other, CredentialProtectionPolicy::None) {
                     if matches!(
                         info,
                         ExtensionInfo::RequireEnforceValue | ExtensionInfo::RequireDontEnforceValue
                     ) {
                         Err(ExtensionErr::MissingCredProtect)
                     } else {
                         Ok(())
                     }
                 } else {
                     Ok(())
                 }
             }
             Self::UserVerificationOptionalWithCredentialIdList(_, info) => match info {
                 ExtensionInfo::RequireEnforceValue => match other {
                     CredentialProtectionPolicy::None => Err(ExtensionErr::MissingCredProtect),
                     CredentialProtectionPolicy::UserVerificationOptional => {
                         Err(ExtensionErr::InvalidCredProtectValue(self, other))
                     }
                     CredentialProtectionPolicy::UserVerificationOptionalWithCredentialIdList
                     | CredentialProtectionPolicy::UserVerificationRequired => Ok(()),
                 },
                 ExtensionInfo::RequireDontEnforceValue => {
                     if matches!(other, CredentialProtectionPolicy::None) {
                         Err(ExtensionErr::MissingCredProtect)
                     } else {
                         Ok(())
                     }
                 }
                 ExtensionInfo::AllowEnforceValue => {
                     if matches!(other, CredentialProtectionPolicy::UserVerificationOptional) {
                         Err(ExtensionErr::InvalidCredProtectValue(self, other))
                     } else {
                         Ok(())
                     }
                 }
                 ExtensionInfo::AllowDontEnforceValue => Ok(()),
             },
             Self::UserVerificationRequired(_, info) => match info {
                 ExtensionInfo::RequireEnforceValue => match other {
                     CredentialProtectionPolicy::None => Err(ExtensionErr::MissingCredProtect),
                     CredentialProtectionPolicy::UserVerificationOptional
                     | CredentialProtectionPolicy::UserVerificationOptionalWithCredentialIdList => {
                         Err(ExtensionErr::InvalidCredProtectValue(self, other))
                     }
                     CredentialProtectionPolicy::UserVerificationRequired => Ok(()),
                 },
                 ExtensionInfo::RequireDontEnforceValue => {
                     if matches!(other, CredentialProtectionPolicy::None) {
                         Err(ExtensionErr::MissingCredProtect)
                     } else {
                         Ok(())
                     }
                 }
                 ExtensionInfo::AllowEnforceValue => {
                     if matches!(
                         other,
                         CredentialProtectionPolicy::None
                             | CredentialProtectionPolicy::UserVerificationRequired
                     ) {
                         Ok(())
                     } else {
                         Err(ExtensionErr::InvalidCredProtectValue(self, other))
                     }
                 }
                 ExtensionInfo::AllowDontEnforceValue => Ok(()),
             },
         }
     }
 }
 impl Display for CredProtect {
     #[inline]
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match *self {
             Self::None => f.write_str("do not sent a credProtect request"),
             Self::UserVerificationOptional(enforce, info) => {
                 write!(
                     f,
                     "request user verification optional with enforcement {enforce} and {info}"
                 )
             }
             Self::UserVerificationOptionalWithCredentialIdList(enforce, info) => write!(
                 f,
                 "user verification optional with credential ID list with enforcement {enforce} and {info}"
             ),
             Self::UserVerificationRequired(enforce, info) => {
                 write!(
                     f,
                     "user verification required with enforcement {enforce} and {info}"
                 )
             }
         }
     }
 }
 /// [`COSEAlgorithmIdentifier`](https://www.w3.org/TR/webauthn-3/#typedefdef-cosealgorithmidentifier).
 ///
 /// Note the order of variants is the following:
 ///
 /// [`Self::Mldsa87`] `<` [`Self::Mldsa65`] `<` [`Self::Mldsa44`] `<` [`Self::Eddsa`] `<` [`Self::Es256`]
 /// `<` [`Self::Es384`] `<` [`Self::Rs256`].
 ///
 /// This is relevant for [`CoseAlgorithmIdentifiers`]. For example a `CoseAlgorithmIdentifiers`
 /// that contains `Self::Mldsa87` will prioritize it over all others.
 #[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
 pub enum CoseAlgorithmIdentifier {
     /// [ML-DSA-87](https://www.iana.org/assignments/cose/cose.xhtml#algorithms).
     Mldsa87,
     /// [ML-DSA-65](https://www.iana.org/assignments/cose/cose.xhtml#algorithms).
     Mldsa65,
     /// [ML-DSA-44](https://www.iana.org/assignments/cose/cose.xhtml#algorithms).
     Mldsa44,
     /// [EdDSA](https://www.iana.org/assignments/cose/cose.xhtml#algorithms).
     ///
     /// Note that Ed25519 must be used for the `crv` parameter
     /// [per the spec](https://www.w3.org/TR/webauthn-3/#sctn-alg-identifier).
     Eddsa,
     /// [ES256](https://www.iana.org/assignments/cose/cose.xhtml#algorithms).
     ///
     /// Note the uncompressed form must be used and P-256 must be used for the `crv` parameter
     /// [per the spec](https://www.w3.org/TR/webauthn-3/#sctn-alg-identifier).
     Es256,
     /// [ES384](https://www.iana.org/assignments/cose/cose.xhtml#algorithms).
     ///
     /// Note the uncompressed form must be used and P-384 must be used for the `crv` parameter
     /// [per the spec](https://www.w3.org/TR/webauthn-3/#sctn-alg-identifier).
     Es384,
     /// [RS256](https://www.iana.org/assignments/cose/cose.xhtml#algorithms).
     Rs256,
 }
 impl CoseAlgorithmIdentifier {
     /// Transforms `self` into a `u8`.
     const fn to_u8(self) -> u8 {
         match self {
             Self::Mldsa87 => 0x1,
             Self::Mldsa65 => 0x2,
             Self::Mldsa44 => 0x4,
             Self::Eddsa => 0x8,
             Self::Es256 => 0x10,
             Self::Es384 => 0x20,
             Self::Rs256 => 0x40,
         }
     }
 }
 impl PartialEq<&Self> for CoseAlgorithmIdentifier {
     #[inline]
     fn eq(&self, other: &&Self) -> bool {
         *self == **other
     }
 }
 impl PartialEq<CoseAlgorithmIdentifier> for &CoseAlgorithmIdentifier {
     #[inline]
     fn eq(&self, other: &CoseAlgorithmIdentifier) -> bool {
         **self == *other
     }
 }
 /// Non-empty ordered set of [`CoseAlgorithmIdentifier`]s.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct CoseAlgorithmIdentifiers(u8);
 impl CoseAlgorithmIdentifiers {
     /// Contains all [`CoseAlgorithmIdentifier`]s.
     pub const ALL: Self = Self(0)
         .add(CoseAlgorithmIdentifier::Mldsa87)
         .add(CoseAlgorithmIdentifier::Mldsa65)
         .add(CoseAlgorithmIdentifier::Mldsa44)
         .add(CoseAlgorithmIdentifier::Eddsa)
         .add(CoseAlgorithmIdentifier::Es256)
         .add(CoseAlgorithmIdentifier::Es384)
         .add(CoseAlgorithmIdentifier::Rs256);
     /// Returns a `CoseAlgorithmIdentifiers` containing all `CoseAlgorithmIdentifier`s in `self` plus `alg`.
     const fn add(self, alg: CoseAlgorithmIdentifier) -> Self {
         Self(self.0 | alg.to_u8())
     }
     /// Returns a copy of `self` with `alg` removed if there would be at least one `CoseAlgorithmIdentifier`
     /// remaining; otherwise returns `self`.
     #[inline]
     #[must_use]
     pub const fn remove(self, alg: CoseAlgorithmIdentifier) -> Self {
         let val = alg.to_u8();
         if self.0 == val {
             self
         } else {
             Self(self.0 & !val)
         }
     }
     /// Returns `true` iff `self` contains `alg`.
     #[inline]
     #[must_use]
     pub const fn contains(self, alg: CoseAlgorithmIdentifier) -> bool {
         let val = alg.to_u8();
         self.0 & val == val
     }
     /// Validates `other` is allowed based on `self`.
     const fn validate(self, other: UncompressedPubKey<'_>) -> Result<(), RegCeremonyErr> {
         if match other {
             UncompressedPubKey::MlDsa87(_) => self.contains(CoseAlgorithmIdentifier::Mldsa87),
             UncompressedPubKey::MlDsa65(_) => self.contains(CoseAlgorithmIdentifier::Mldsa65),
             UncompressedPubKey::MlDsa44(_) => self.contains(CoseAlgorithmIdentifier::Mldsa44),
             UncompressedPubKey::Ed25519(_) => self.contains(CoseAlgorithmIdentifier::Eddsa),
             UncompressedPubKey::P256(_) => self.contains(CoseAlgorithmIdentifier::Es256),
             UncompressedPubKey::P384(_) => self.contains(CoseAlgorithmIdentifier::Es384),
             UncompressedPubKey::Rsa(_) => self.contains(CoseAlgorithmIdentifier::Rs256),
         } {
             Ok(())
         } else {
             Err(RegCeremonyErr::PublicKeyAlgorithmMismatch)
         }
     }
 }
 impl Default for CoseAlgorithmIdentifiers {
     /// Returns [`Self::ALL`].
     #[inline]
     fn default() -> Self {
         Self::ALL
     }
 }
 /// Four to sixty-three inclusively.
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
 #[repr(u8)]
 pub enum FourToSixtyThree {
     /// 4.
     Four = 4,
     /// 5.
     Five,
     /// 6.
     Six,
     /// 7.
     Seven,
     /// 8.
     Eight,
     /// 9.
     Nine,
     /// 10.
     Ten,
     /// 11.
     Eleven,
     /// 12.
     Twelve,
     /// 13.
     Thirteen,
     /// 14.
     Fourteen,
     /// 15.
     Fifteen,
     /// 16.
     Sixteen,
     /// 17.
     Seventeen,
     /// 18.
     Eighteen,
     /// 19.
     Nineteen,
     /// 20.
     Twenty,
     /// 21.
     TwentyOne,
     /// 22.
     TwentyTwo,
     /// 23.
     TwentyThree,
     /// 24.
     TwentyFour,
     /// 25.
     TwentyFive,
     /// 26.
     TwentySix,
     /// 27.
     TwentySeven,
     /// 28.
     TwentyEight,
     /// 29.
     TwentyNine,
     /// 30.
     Thirty,
     /// 31.
     ThirtyOne,
     /// 32.
     ThirtyTwo,
     /// 33.
     ThirtyThree,
     /// 34.
     ThirtyFour,
     /// 35.
     ThirtyFive,
     /// 36.
     ThirtySix,
     /// 37.
     ThirtySeven,
     /// 38.
     ThirtyEight,
     /// 39.
     ThirtyNine,
     /// 40.
     Fourty,
     /// 41.
     FourtyOne,
     /// 42.
     FourtyTwo,
     /// 43.
     FourtyThree,
     /// 44.
     FourtyFour,
     /// 45.
     FourtyFive,
     /// 46.
     FourtySix,
     /// 47.
     FourtySeven,
     /// 48.
     FourtyEight,
     /// 49.
     FourtyNine,
     /// 50.
     Fifty,
     /// 51.
     FiftyOne,
     /// 52.
     FiftyTwo,
     /// 53.
     FiftyThree,
     /// 54.
     FiftyFour,
     /// 55.
     FiftyFive,
     /// 56.
     FiftySix,
     /// 57.
     FiftySeven,
     /// 58.
     FiftyEight,
     /// 59.
     FiftyNine,
     /// 60.
     Sixty,
     /// 61.
     SixtyOne,
     /// 62.
     SixtyTwo,
     /// 63.
     SixtyThree,
 }
 impl FourToSixtyThree {
     /// Returns the equivalent `u8`.
     #[expect(clippy::as_conversions, reason = "comment justifies correctness")]
     #[inline]
     #[must_use]
     pub const fn into_u8(self) -> u8 {
         // This is correct since `Self` is `repr(u8)`, and the initial discriminant has the value `4`
         // and subsequent discriminants are implicitly incremented by 1.
         self as u8
     }
     /// Returns `Some` representing `val` iff `val` is inclusively between 4 and 63.
     #[expect(unsafe_code, reason = "comment justifies correctness")]
     #[inline]
     #[must_use]
     pub const fn from_u8(val: u8) -> Option<Self> {
         match val {
             0..=3 | 64.. => None,
             _ => {
                 // SAFETY:
                 // `val` is inclusively between 4 and 63, and `Self` is `repr(u8)`; thus this
                 // is safe and correct.
                 Some(unsafe { mem::transmute::<u8, Self>(val) })
             }
         }
     }
 }
 impl Display for FourToSixtyThree {
     #[inline]
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         self.into_u8().fmt(f)
     }
 }
 impl From<FourToSixtyThree> for u8 {
     #[inline]
     fn from(value: FourToSixtyThree) -> Self {
         value.into_u8()
     }
 }
 impl Default for FourToSixtyThree {
     #[inline]
     fn default() -> Self {
         Self::Four
     }
 }
 /// The [defined extensions](https://www.w3.org/TR/webauthn-3/#sctn-defined-extensions) to send to the client.
 #[derive(Clone, Copy, Debug)]
 pub struct Extension<'prf_first, 'prf_second> {
     /// [`credProps`](https://www.w3.org/TR/webauthn-3/#sctn-authenticator-credential-properties-extension).
     ///
     /// The best one can do to ensure a server-side credential is created is by sending
     /// [`ResidentKeyRequirement::Discouraged`]; however authenticators are still allowed
     /// to create a client-side credential. To more definitively check that a server-side credential is
     /// created, send this extension. Note that it can be difficult to impossible for a client/user agent to
     /// know that a server-side credential is created; thus even when the response is
     /// `Some(CredentialPropertiesOutput { rk: Some(false) })`, a client-side/"resident" credential could still
     /// have been created. One may have better luck checking if [`AuthTransports::contains`]
     /// [`AuthenticatorTransport::Internal`] and using that as an indicator if a client-side credential was created.
     ///
     /// In the event [`ClientExtensionsOutputs::cred_props`] is `Some(CredentialPropertiesOutput { rk: Some(false) })`
     /// and [`ResidentKeyRequirement::Required`] was sent, an error will happen regardless of this value.
     pub cred_props: Option<ExtensionReq>,
     /// [`credProtect`](https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#sctn-credProtect-extension).
     pub cred_protect: CredProtect,
     /// [`minPinLength`](https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#sctn-minpinlength-extension).
     ///
     /// When the value is enforced, that corresponds to
     /// [`minPinLength`](https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#sctn-minpinlength-extension)
     /// in [`extensions`](https://www.w3.org/TR/webauthn-3/#authdata-extensions) set to a value at least as large
     /// as the contained `FourToSixtyThree`.
     pub min_pin_length: Option<(FourToSixtyThree, ExtensionInfo)>,
     /// [`prf`](https://www.w3.org/TR/webauthn-3/#prf-extension).
     ///
     /// When the value is enforced, that corresponds to
     /// [`enabled`](https://www.w3.org/TR/webauthn-3/#dom-authenticationextensionsprfoutputs-enabled) set to `true`.
     /// In contrast [`results`](https://www.w3.org/TR/webauthn-3/#dom-authenticationextensionsprfoutputs-results)
     /// must not exist, be `null`, or be an
     /// [`AuthenticationExtensionsPRFValues`](https://www.w3.org/TR/webauthn-3/#dictdef-authenticationextensionsprfvalues)
     /// such that [`first`](https://www.w3.org/TR/webauthn-3/#dom-authenticationextensionsprfvalues-first) is `null`
     /// and [`second`](https://www.w3.org/TR/webauthn-3/#dom-authenticationextensionsprfvalues-second) does not
     /// exist or is `null`. This is to ensure the decrypted outputs stay on the client.
     ///
     /// Note some authenticators can only enable `prf` during registration (e.g., CTAP authenticators that only
     /// support
     /// [`hmac-secret`](https://fidoalliance.org/specs/fido-v2.2-ps-20250228/fido-client-to-authenticator-protocol-v2.2-ps-20250228.html#sctn-hmac-secret-extension)
     /// and not
     /// [`hmac-secret-mc`](https://fidoalliance.org/specs/fido-v2.2-ps-20250228/fido-client-to-authenticator-protocol-v2.2-ps-20250228.html#sctn-hmac-secret-make-cred-extension));
     /// thus the value of `PrfInput` is ignored and only used as a signal to enable `prf`. For many such
     /// authenticators, not using this extension during registration will not preclude them from being used during
     /// authentication; however it is still encouraged to use the extension during registration since some
     /// authenticators actually require it.
     ///
     /// When the underlying credential is expected to be used during discoverable requests, it is likely that
     /// `'prf_first` will be `'static` and [`PrfInput::second`] is `None` since one will not be able to
     /// realistically rotate the underlying inputs and further the same input will likely be used for all credentials.
     /// For credentials intended to be used during non-discoverable requests, however, one is encouraged to rotate
     /// the inputs and have unique values for each credential.
     pub prf: Option<(PrfInput<'prf_first, 'prf_second>, ExtensionInfo)>,
 }
 impl<'prf_first, 'prf_second> Extension<'prf_first, 'prf_second> {
     /// Returns an empty `Extension`.
     #[inline]
     #[must_use]
     pub const fn none() -> Self {
         Self {
             cred_props: None,
             cred_protect: CredProtect::None,
             min_pin_length: None,
             prf: None,
         }
     }
     /// Same as [`Self::none`] except [`Self::cred_props`] is `Some` containing `req`.
     #[inline]
     #[must_use]
     pub const fn with_cred_props(req: ExtensionReq) -> Self {
         Self {
             cred_props: Some(req),
             ..Self::none()
         }
     }
     /// Same as [`Self::none`] except [`Self::cred_protect`] is `cred_protect`.
     #[inline]
     #[must_use]
     pub const fn with_cred_protect(cred_protect: CredProtect) -> Self {
         Self {
             cred_protect,
             ..Self::none()
         }
     }
     /// Same as [`Self::none`] except [`Self::min_pin_length`] is `Some` containing `min_len` and `info`.
     #[inline]
     #[must_use]
     pub const fn with_min_pin_length(min_len: FourToSixtyThree, info: ExtensionInfo) -> Self {
         Self {
             min_pin_length: Some((min_len, info)),
             ..Self::none()
         }
     }
     /// Same as [`Self::none`] except [`Self::prf`] is `Some` containing `input` and `info`.
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[inline]
     #[must_use]
     pub const fn with_prf<'a: 'prf_first, 'b: 'prf_second>(
         input: PrfInput<'a, 'b>,
         info: ExtensionInfo,
     ) -> Self {
         Self {
             prf: Some((input, info)),
             ..Self::none()
         }
     }
 }
 impl Default for Extension<'_, '_> {
     /// Same as [`Self::none`].
     #[inline]
     fn default() -> Self {
         Self::none()
     }
 }
 #[cfg(test)]
 impl PartialEq for Extension<'_, '_> {
     #[inline]
     fn eq(&self, other: &Self) -> bool {
         self.cred_props == other.cred_props
             && self.cred_protect == other.cred_protect
             && self.min_pin_length == other.min_pin_length
             && self.prf == other.prf
     }
 }
 /// The maximum number of bytes a [`UserHandle`] can be made of per
 /// [WebAuthn](https://www.w3.org/TR/webauthn-3/#user-handle).
 pub const USER_HANDLE_MAX_LEN: usize = 64;
 /// The minimum number of bytes a [`UserHandle`] can be made of per
 /// [WebAuthn](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialuserentity-id).
 pub const USER_HANDLE_MIN_LEN: usize = 1;
 /// A [user handle](https://www.w3.org/TR/webauthn-3/#user-handle) that is made up of
 /// [`USER_HANDLE_MIN_LEN`]–[`USER_HANDLE_MAX_LEN`] bytes.
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct UserHandle<const LEN: usize>([u8; LEN]);
 impl<const LEN: usize> UserHandle<LEN> {
     /// Returns the contained data as a `slice`.
     #[inline]
     #[must_use]
     pub const fn as_slice(&self) -> &[u8] {
         self.0.as_slice()
     }
     /// Returns the contained data as a shared reference to the array.
     #[inline]
     #[must_use]
     pub const fn as_array(&self) -> &[u8; LEN] {
         &self.0
     }
     /// Returns the contained data.
     #[inline]
     #[must_use]
     pub const fn into_array(self) -> [u8; LEN] {
         self.0
     }
 }
 /// Implements [`Default`] for [`UserHandle`] of array of length of the passed `usize` literal.
 ///
 /// Only [`USER_HANDLE_MIN_LEN`]–[`USER_HANDLE_MAX_LEN`] inclusively are allowed to be passed.
 macro_rules! user {
     ( $( $x:literal),* ) => {
         $(
 impl Default for UserHandle<$x> {
     #[inline]
     fn default() -> Self {
         let mut data = [0; $x];
         rand::fill(data.as_mut_slice());
         Self(data)
     }
 }
         )*
     };
 }
 // MUST only pass [`USER_HANDLE_MIN_LEN`]–[`USER_HANDLE_MAX_LEN`] inclusively.
 user!(
     1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26,
     27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
     51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64
 );
 impl<const LEN: usize> UserHandle<LEN>
 where
     Self: Default,
 {
     /// Returns a new `UserHandle` based on `LEN` randomly-generated [`u8`]s.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::register::{UserHandle, UserHandle64, USER_HANDLE_MIN_LEN, USER_HANDLE_MAX_LEN};
     /// assert_eq!(
     ///     UserHandle::<USER_HANDLE_MIN_LEN>::new()
     ///         .as_ref()
     ///         .len(),
     ///     1
     /// );
     /// // The probability of an all-zero `UserHandle` being generated (assuming a good entropy
     /// // source) is 2^-512 ≈ 7.5 x 10^-155.
     /// assert_ne!(
     ///     UserHandle64::new().as_ref(),
     ///     [0; USER_HANDLE_MAX_LEN]
     /// );
     /// ```
     #[inline]
     #[must_use]
     pub fn new() -> Self {
         Self::default()
     }
 }
 impl<const LEN: usize> AsRef<[u8]> for UserHandle<LEN> {
     #[inline]
     fn as_ref(&self) -> &[u8] {
         self.as_slice()
     }
 }
 impl<const LEN: usize> Borrow<[u8]> for UserHandle<LEN> {
     #[inline]
     fn borrow(&self) -> &[u8] {
         self.as_slice()
     }
 }
 impl<const LEN: usize> PartialEq<&Self> for UserHandle<LEN> {
     #[inline]
     fn eq(&self, other: &&Self) -> bool {
         *self == **other
     }
 }
 impl<const LEN: usize> PartialEq<UserHandle<LEN>> for &UserHandle<LEN> {
     #[inline]
     fn eq(&self, other: &UserHandle<LEN>) -> bool {
         **self == *other
     }
 }
 impl<const LEN: usize> From<UserHandle<LEN>> for [u8; LEN] {
     #[inline]
     fn from(value: UserHandle<LEN>) -> Self {
         value.into_array()
     }
 }
 impl<'a: 'b, 'b, const LEN: usize> From<&'a UserHandle<LEN>> for &'b [u8; LEN] {
     #[inline]
     fn from(value: &'a UserHandle<LEN>) -> Self {
         value.as_array()
     }
 }
 /// `UserHandle` that is based on the [spec recommendation](https://www.w3.org/TR/webauthn-3/#user-handle).
 pub type UserHandle64 = UserHandle<USER_HANDLE_MAX_LEN>;
 /// `UserHandle` that is based on 16 bytes.
 ///
 /// While not the recommended size like [`UserHandle64`], 16 bytes is common for many deployments since
 /// it's the same size as [Universally Unique IDentifiers (UUIDs)](https://www.rfc-editor.org/rfc/rfc9562).
 pub type UserHandle16 = UserHandle<16>;
 impl UserHandle16 {
     /// Same as [`Self::new`] except 6 bits of metadata is encoded to conform with
     /// [UUID Version 4](https://www.rfc-editor.org/rfc/rfc9562#name-uuid-version-4).
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::register::UserHandle16;
     /// assert!(UserHandle16::new_uuid_v4().is_uuid_v4());
     /// ```
     #[inline]
     #[must_use]
     pub fn new_uuid_v4() -> Self {
         let mut this = Self::new();
         // The first 4 bits of the 6th octet (0-based index) represents the UUID version (i.e., 4).
         // We first 0-out the version bits retaining the other 4 bits, then set the version bits to 4.
         this.0[6] = (this.0[6] & 0x0F) | 0x40;
         // The first 2 bits of the 8th octet (0-based index) represents the UUID variant (i.e., 8,9,A,B)
         // which is defined to be 2.
         // We first 0-out the variant bits retaining the other 6 bits, then set the variant bits to 2.
         this.0[8] = (this.0[8] & 0x3F) | 0x80;
         this
     }
     /// Returns `true` iff `self` is a valid
     /// [UUID Version 4](https://www.rfc-editor.org/rfc/rfc9562#name-uuid-version-4).
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::register::UserHandle16;
     /// assert!(UserHandle16::new_uuid_v4().is_uuid_v4());
     /// let mut user = UserHandle16::new_uuid_v4().into_array();
     /// user[6] = 255;
     /// # #[cfg(feature = "custom")]
     /// assert!(!UserHandle16::from(user).is_uuid_v4());
     /// ```
     #[inline]
     #[must_use]
     pub const fn is_uuid_v4(&self) -> bool {
         // The first 4 bits of the 6th octet (0-based index) represents the UUID version (i.e., 4).
         // The first 2 bits of the 8th octet (0-based index) represents the UUID variant (i.e., 8,9,A,B) which
         // is defined to be 2.
         self.0[6] >> 4 == 0x4 && self.0[8] >> 6 == 0x2
     }
     /// Returns `Some` containing `uuid_v4` iff `uuid_v4` is a valid
     /// [UUID Version 4](https://www.rfc-editor.org/rfc/rfc9562#name-uuid-version-4).
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::register::UserHandle16;
     /// let mut user = UserHandle16::new_uuid_v4().into_array();
     /// assert!(UserHandle16::from_uuid_v4(user).is_some());
     /// user[8] = 255;
     /// assert!(UserHandle16::from_uuid_v4(user).is_none());
     /// ```
     #[cfg(feature = "custom")]
     #[inline]
     #[must_use]
     pub fn from_uuid_v4(uuid_v4: [u8; 16]) -> Option<Self> {
         let this = Self(uuid_v4);
         this.is_uuid_v4().then_some(this)
     }
 }
 /// [The `PublicKeyCredentialUserEntity`](https://www.w3.org/TR/webauthn-3/#dictdef-publickeycredentialuserentity)
 /// sent to the client.
 #[derive(Clone, Debug)]
 pub struct PublicKeyCredentialUserEntity<'name, 'display_name, 'id, const LEN: usize> {
     /// [`name`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialentity-name).
     ///
     /// Note the spec recommends RPs enforce
     /// [RFC 8265 § 3.4.3](https://www.rfc-editor.org/rfc/rfc8265#section-3.4.3).
     pub name: &'name str,
     /// [`id`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialuserentity-id).
     pub id: &'id UserHandle<LEN>,
     /// [`displayName`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialuserentity-displayname).
     ///
     /// Note the spec recommends RPs enforce [RFC 8266 § 2.3](https://www.rfc-editor.org/rfc/rfc8266#section-2.3)
     /// when this isn't empty.
     pub display_name: &'display_name str,
 }
 /// `PublicKeyCredentialUserEntity` based on a [`UserHandle64`].
 pub type PublicKeyCredentialUserEntity64<'name, 'display_name, 'id> =
     PublicKeyCredentialUserEntity<'name, 'display_name, 'id, USER_HANDLE_MAX_LEN>;
 /// `PublicKeyCredentialUserEntity` based on a [`UserHandle16`].
 pub type PublicKeyCredentialUserEntity16<'name, 'display_name, 'id> =
     PublicKeyCredentialUserEntity<'name, 'display_name, 'id, 16>;
 /// [`ResidentKeyRequirement`](https://www.w3.org/TR/webauthn-3/#enumdef-residentkeyrequirement) sent to the client.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum ResidentKeyRequirement {
     /// [`required`](https://www.w3.org/TR/webauthn-3/#dom-residentkeyrequirement-required).
     Required,
     /// [`discouraged`](https://www.w3.org/TR/webauthn-3/#dom-residentkeyrequirement-discouraged).
     Discouraged,
     /// [`preferred`](https://www.w3.org/TR/webauthn-3/#dom-residentkeyrequirement-preferred).
     Preferred,
 }
 impl AuthenticatorAttachment {
     /// Validates `self` against `other` based on `require_response`.
     const fn validate(self, require_response: bool, other: Self) -> Result<(), RegCeremonyErr> {
         match self {
             Self::None => {
                 if require_response && matches!(other, Self::None) {
                     Err(RegCeremonyErr::MissingAuthenticatorAttachment)
                 } else {
                     Ok(())
                 }
             }
             Self::Platform => match other {
                 Self::None => {
                     if require_response {
                         Err(RegCeremonyErr::MissingAuthenticatorAttachment)
                     } else {
                         Ok(())
                     }
                 }
                 Self::Platform => Ok(()),
                 Self::CrossPlatform => Err(RegCeremonyErr::AuthenticatorAttachmentMismatch),
             },
             Self::CrossPlatform => match other {
                 Self::None => {
                     if require_response {
                         Err(RegCeremonyErr::MissingAuthenticatorAttachment)
                     } else {
                         Ok(())
                     }
                 }
                 Self::CrossPlatform => Ok(()),
                 Self::Platform => Err(RegCeremonyErr::AuthenticatorAttachmentMismatch),
             },
         }
     }
 }
 /// [`AuthenticatorSelectionCriteria`](https://www.w3.org/TR/webauthn-3/#dictionary-authenticatorSelection).
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct AuthenticatorSelectionCriteria {
     /// [`authenticatorAttachment`](https://www.w3.org/TR/webauthn-3/#dom-authenticatorselectioncriteria-authenticatorattachment).
     pub authenticator_attachment: AuthenticatorAttachment,
     /// [`residentKey`](https://www.w3.org/TR/webauthn-3/#dom-authenticatorselectioncriteria-residentkey).
     pub resident_key: ResidentKeyRequirement,
     /// [`userVerification`](https://www.w3.org/TR/webauthn-3/#dom-authenticatorselectioncriteria-userverification).
     pub user_verification: UserVerificationRequirement,
 }
 impl AuthenticatorSelectionCriteria {
     /// Returns an `AuthenticatorSelectionCriteria` useful for passkeys (i.e., [`Self::resident_key`] is set to
     /// [`ResidentKeyRequirement::Required`] and [`Self::user_verification`] is set to
     /// [`UserVerificationRequirement::Required`]).
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::{request::{
     /// #     register::{
     /// #         AuthenticatorSelectionCriteria, ResidentKeyRequirement,
     /// #     },
     /// #     UserVerificationRequirement,
     /// # }, response::AuthenticatorAttachment};
     /// let crit = AuthenticatorSelectionCriteria::passkey();
     /// assert_eq!(crit.authenticator_attachment, AuthenticatorAttachment::None);
     /// assert_eq!(crit.resident_key, ResidentKeyRequirement::Required);
     /// assert_eq!(crit.user_verification, UserVerificationRequirement::Required);
     /// ```
     #[inline]
     #[must_use]
     pub fn passkey() -> Self {
         Self {
             authenticator_attachment: AuthenticatorAttachment::default(),
             resident_key: ResidentKeyRequirement::Required,
             user_verification: UserVerificationRequirement::Required,
         }
     }
     /// Returns an `AuthenticatorSelectionCriteria` useful for second-factor flows (i.e., [`Self::resident_key`]
     /// is set to [`ResidentKeyRequirement::Discouraged`] and [`Self::user_verification`] is set to
     /// [`UserVerificationRequirement::Discouraged`]).
     ///
     /// Note some authenticators require user verification during credential registration (e.g.,
     /// [CTAP 2.0 authenticators](https://fidoalliance.org/specs/fido-v2.0-id-20180227/fido-client-to-authenticator-protocol-v2.0-id-20180227.html#authenticatorMakeCredential)).
     /// When an authenticator supports both CTAP 2.0 and
     /// [Universal 2nd Factor (U2F)](https://fidoalliance.org/specs/fido-u2f-v1.2-ps-20170411/fido-u2f-overview-v1.2-ps-20170411.html#registration-creating-a-key-pair)
     /// protocols, user agents will sometimes fall back to U2F when `UserVerificationRequirement::Discouraged`
     /// is requested since the latter allows for registration without user verification. If the user agent does not
     /// do this, then users will have an inconsistent experience when authenticating an already-registered
     /// credential. If this is undesirable, one can use [`UserVerificationRequirement::Required`] for this and
     /// [`PublicKeyCredentialRequestOptions::user_verification`] at the expense of requiring a user to verify
     /// themselves twice: once for the first factor and again here.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::{request::{
     /// #     register::{
     /// #         AuthenticatorSelectionCriteria, ResidentKeyRequirement,
     /// #     },
     /// #     UserVerificationRequirement,
     /// # }, response::AuthenticatorAttachment};
     /// let crit = AuthenticatorSelectionCriteria::second_factor();
     /// assert_eq!(crit.authenticator_attachment, AuthenticatorAttachment::None);
     /// assert_eq!(crit.resident_key, ResidentKeyRequirement::Discouraged);
     /// assert_eq!(crit.user_verification, UserVerificationRequirement::Discouraged);
     /// ```
     #[inline]
     #[must_use]
     pub fn second_factor() -> Self {
         Self {
             authenticator_attachment: AuthenticatorAttachment::default(),
             resident_key: ResidentKeyRequirement::Discouraged,
             user_verification: UserVerificationRequirement::Discouraged,
         }
     }
     /// Ensures a client-side credential was created when applicable. Also enforces `auth_attachment` when
     /// applicable.
     const fn validate(
         self,
         require_auth_attachment: bool,
         auth_attachment: AuthenticatorAttachment,
     ) -> Result<(), RegCeremonyErr> {
         self.authenticator_attachment
             .validate(require_auth_attachment, auth_attachment)
     }
 }
 /// Helper that verifies the overlap of [`CredentialCreationOptions::start_ceremony`] and
 /// [`RegistrationServerState::decode`].
 const fn validate_options_helper(
     auth_crit: AuthenticatorSelectionCriteria,
     extensions: ServerExtensionInfo,
 ) -> Result<(), CreationOptionsErr> {
     if matches!(
         auth_crit.user_verification,
         UserVerificationRequirement::Required
     ) {
         Ok(())
     } else if matches!(
         extensions.cred_protect,
         CredProtect::UserVerificationRequired(_, _)
     ) {
         Err(CreationOptionsErr::CredProtectRequiredWithoutUserVerification)
     } else {
         Ok(())
     }
 }
 /// The [`CredentialCreationOptions`](https://www.w3.org/TR/credential-management-1/#dictdef-credentialcreationoptions)
 /// to send to the client when registering a new credential.
 ///
 /// Upon saving the [`RegistrationServerState`] returned from [`Self::start_ceremony`], one MUST send
 /// [`RegistrationClientState`] to the client ASAP. After receiving the newly created [`Registration`], it is
 /// validated using [`RegistrationServerState::verify`].
 #[derive(Debug)]
 pub struct CredentialCreationOptions<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     const USER_LEN: usize,
 > {
     /// [`mediation`](https://www.w3.org/TR/credential-management-1/#dom-credentialcreationoptions-mediation).
     ///
     /// Note if this is [`CredentialMediationRequirement::Conditional`], one may want to ensure
     /// [`AuthenticatorSelectionCriteria::user_verification`] is not [`UserVerificationRequirement::Required`]
     /// since some authenticators cannot enforce user verification during registration ceremonies when conditional
     /// mediation is used. Do note that in the event passkeys are to be created, one may want to set
     /// [`AuthenticationVerificationOptions::update_uv`] to `true` since [`Flag::user_verified`] will
     /// potentially be `false`.
     pub mediation: CredentialMediationRequirement,
     /// `public-key` [credential type](https://www.w3.org/TR/credential-management-1/#sctn-cred-type-registry).
     pub public_key: PublicKeyCredentialCreationOptions<
         'rp_id,
         'user_name,
         'user_display_name,
         'user_id,
         'prf_first,
         'prf_second,
         USER_LEN,
     >,
 }
 impl<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     const USER_LEN: usize,
 >
     CredentialCreationOptions<
         'rp_id,
         'user_name,
         'user_display_name,
         'user_id,
         'prf_first,
         'prf_second,
         USER_LEN,
     >
 {
     /// Sets [`Self::mediation`] to [`CredentialMediationRequirement::default`] and
     /// [`Self::public_key`] to [`PublicKeyCredentialCreationOptions::passkey`].
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[inline]
     #[must_use]
     pub fn passkey<'a: 'rp_id, 'b: 'user_name, 'c: 'user_display_name, 'd: 'user_id>(
         rp_id: &'a RpId,
         user: PublicKeyCredentialUserEntity<'b, 'c, 'd, USER_LEN>,
         exclude_credentials: Vec<PublicKeyCredentialDescriptor<Box<[u8]>>>,
     ) -> Self {
         Self {
             mediation: CredentialMediationRequirement::default(),
             public_key: PublicKeyCredentialCreationOptions::passkey(
                 rp_id,
                 user,
                 exclude_credentials,
             ),
         }
     }
     /// Sets [`Self::mediation`] to [`CredentialMediationRequirement::default`] and
     /// [`Self::public_key`] to [`PublicKeyCredentialCreationOptions::second_factor`].
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[inline]
     #[must_use]
     pub fn second_factor<'a: 'rp_id, 'b: 'user_name, 'c: 'user_display_name, 'd: 'user_id>(
         rp_id: &'a RpId,
         user: PublicKeyCredentialUserEntity<'b, 'c, 'd, USER_LEN>,
         exclude_credentials: Vec<PublicKeyCredentialDescriptor<Box<[u8]>>>,
     ) -> Self {
         let mut opts = Self::passkey(rp_id, user, exclude_credentials);
         opts.public_key.authenticator_selection = AuthenticatorSelectionCriteria::second_factor();
         opts.public_key.extensions.cred_props = Some(ExtensionReq::Allow);
         opts.public_key.extensions.cred_protect =
             CredProtect::UserVerificationOptionalWithCredentialIdList(
                 false,
                 ExtensionInfo::AllowEnforceValue,
             );
         opts
     }
     /// Begins the [registration ceremony](https://www.w3.org/TR/webauthn-3/#registration-ceremony) consuming
     /// `self`. Note that the expiration [`Instant`]/[`SystemTime`] is saved, so `RegistrationClientState` MUST be
     /// sent ASAP. In order to complete registration, the returned `RegistrationServerState` MUST be saved so that
     /// it can later be used to verify the new credential with [`RegistrationServerState::verify`].
     ///
     /// # Errors
     ///
     /// Errors iff `self` contains incompatible configuration.
     ///
     /// # Examples
     ///
     /// ```
     /// # #[cfg(not(feature = "serializable_server_state"))]
     /// # use std::time::Instant;
     /// # #[cfg(not(feature = "serializable_server_state"))]
     /// # use webauthn_rp::request::TimedCeremony as _;
     /// # use webauthn_rp::request::{
     /// #     register::{CredentialCreationOptions, PublicKeyCredentialUserEntity, UserHandle64},
     /// #     AsciiDomain, RpId
     /// # };
     /// # #[cfg(not(feature = "serializable_server_state"))]
     /// assert!(
     ///     CredentialCreationOptions::passkey(
     ///         &RpId::Domain(AsciiDomain::try_from("example.com".to_owned())?),
     ///         PublicKeyCredentialUserEntity {
     ///             name: "bernard.riemann",
     ///             id: &UserHandle64::new(),
     ///             display_name: "Georg Friedrich Bernhard Riemann",
     ///         },
     ///         Vec::new()
     ///     ).start_ceremony()?.0.expiration() > Instant::now()
     /// );
     /// # Ok::<_, webauthn_rp::AggErr>(())
     /// ```
     #[inline]
     pub fn start_ceremony(
         mut self,
     ) -> Result<
         (
             RegistrationServerState<USER_LEN>,
             RegistrationClientState<
                 'rp_id,
                 'user_name,
                 'user_display_name,
                 'user_id,
                 'prf_first,
                 'prf_second,
                 USER_LEN,
             >,
         ),
         CreationOptionsErr,
     > {
         let extensions = self.public_key.extensions.into();
         validate_options_helper(self.public_key.authenticator_selection, extensions).and_then(
             |()| {
                 match self
                     .public_key
                     .authenticator_selection
                     .authenticator_attachment
                 {
                     AuthenticatorAttachment::None => Ok(()),
                     AuthenticatorAttachment::Platform => {
                         if self.public_key.hints.contains_cross_platform_hints() {
                             Err(CreationOptionsErr::HintsIncompatibleWithAuthAttachment)
                         } else {
                             Ok(())
                         }
                     }
                     AuthenticatorAttachment::CrossPlatform => {
                         if self.public_key.hints.contains_platform_hints() {
                             Err(CreationOptionsErr::HintsIncompatibleWithAuthAttachment)
                         } else {
                             Ok(())
                         }
                     }
                 }
                 .and_then(|()| {
                     #[cfg(not(feature = "serializable_server_state"))]
                     let now = Instant::now();
                     #[cfg(feature = "serializable_server_state")]
                     let now = SystemTime::now();
                     now.checked_add(Duration::from_millis(
                         NonZeroU64::from(self.public_key.timeout).get(),
                     ))
                     .ok_or(CreationOptionsErr::InvalidTimeout)
                     .map(|expiration| {
                         // We remove duplicates. The order has no significance, so this is OK.
                         self.public_key
                             .exclude_credentials
                             .sort_unstable_by(|a, b| a.id.as_ref().cmp(b.id.as_ref()));
                         self.public_key
                             .exclude_credentials
                             .dedup_by(|a, b| a.id.as_ref() == b.id.as_ref());
                         (
                             RegistrationServerState {
                                 mediation: self.mediation,
                                 challenge: SentChallenge(self.public_key.challenge.0),
                                 pub_key_cred_params: self.public_key.pub_key_cred_params,
                                 authenticator_selection: self.public_key.authenticator_selection,
                                 extensions,
                                 expiration,
                                 user_id: *self.public_key.user.id,
                             },
                             RegistrationClientState(self),
                         )
                     })
                 })
             },
         )
     }
 }
 /// `CredentialCreationOptions` based on a [`UserHandle64`].
 pub type CredentialCreationOptions64<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
 > = CredentialCreationOptions<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     USER_HANDLE_MAX_LEN,
 >;
 /// `CredentialCreationOptions` based on a [`UserHandle16`].
 pub type CredentialCreationOptions16<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
 > = CredentialCreationOptions<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     16,
 >;
 /// The [`PublicKeyCredentialCreationOptions`](https://www.w3.org/TR/webauthn-3/#dictdef-publickeycredentialcreationoptions)
 /// to send to the client when registering a new credential.
 #[derive(Debug)]
 pub struct PublicKeyCredentialCreationOptions<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     const USER_LEN: usize,
 > {
     /// [`rp`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-rp).
     pub rp_id: &'rp_id RpId,
     /// [`user`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-user).
     pub user: PublicKeyCredentialUserEntity<'user_name, 'user_display_name, 'user_id, USER_LEN>,
     /// [`challenge`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-challenge).
     pub challenge: Challenge,
     /// [`pubKeyCredParams`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-pubkeycredparams).
     pub pub_key_cred_params: CoseAlgorithmIdentifiers,
     /// [`timeout`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-timeout).
     ///
     /// Note we require a positive value despite the spec allowing an optional nonnegative value. This jives
     /// with the fact that in-memory storage is required when `serializable_server_state` is not enabled
     /// when attesting credentials as no timeout would make out-of-memory (OOM) conditions more likely.
     pub timeout: NonZeroU32,
     /// [`excludeCredentials`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-excludecredentials).
     pub exclude_credentials: Vec<PublicKeyCredentialDescriptor<Box<[u8]>>>,
     /// [`authenticatorSelection`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-authenticatorselection).
     pub authenticator_selection: AuthenticatorSelectionCriteria,
     /// [`hints`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-hints).
     pub hints: Hints,
     /// [`extensions`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-extensions).
     pub extensions: Extension<'prf_first, 'prf_second>,
 }
 impl<'rp_id, 'user_name, 'user_display_name, 'user_id, const USER_LEN: usize>
     PublicKeyCredentialCreationOptions<
         'rp_id,
         'user_name,
         'user_display_name,
         'user_id,
         '_,
         '_,
         USER_LEN,
     >
 {
     /// Most deployments of passkeys should use this function. Specifically deployments that are both userless and
     /// passwordless and desire multi-factor authentication (MFA) to be done entirely on the authenticator. It
     /// is important `exclude_credentials` contains the information for _all_ [`RegisteredCredential`]s registered to
     /// [`PublicKeyCredentialUserEntity::id`] to avoid accidentally overwriting existing credentials that
     /// have been previously registered.
     ///
     /// Creates a `PublicKeyCredentialCreationOptions` that requires the authenticator to create a client-side
     /// discoverable credential enforcing any form of user verification. [`Self::timeout`] is [`FIVE_MINUTES`].
     /// [`Extension::cred_protect`] with [`CredProtect::UserVerificationRequired`] with `false` and
     /// [`ExtensionInfo::AllowEnforceValue`] is used.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{
     /// #     register::{
     /// #         PublicKeyCredentialCreationOptions, PublicKeyCredentialUserEntity, UserHandle64
     /// #     },
     /// #     AsciiDomain, RpId, UserVerificationRequirement
     /// # };
     /// assert!(matches!(
     ///     PublicKeyCredentialCreationOptions::passkey(
     ///         &RpId::Domain(AsciiDomain::try_from("example.com".to_owned())?),
     ///         PublicKeyCredentialUserEntity {
     ///             name: "archimedes.of.syracuse",
     ///             id: &UserHandle64::new(),
     ///             display_name: "Αρχιμήδης ο Συρακούσιος",
     ///         },
     ///         Vec::new()
     ///     )
     ///     .authenticator_selection.user_verification, UserVerificationRequirement::Required
     /// ));
     /// # Ok::<_, webauthn_rp::AggErr>(())
     /// ```
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[inline]
     #[must_use]
     pub fn passkey<'a: 'rp_id, 'b: 'user_name, 'c: 'user_display_name, 'd: 'user_id>(
         rp_id: &'a RpId,
         user: PublicKeyCredentialUserEntity<'b, 'c, 'd, USER_LEN>,
         exclude_credentials: Vec<PublicKeyCredentialDescriptor<Box<[u8]>>>,
     ) -> Self {
         Self {
             rp_id,
             user,
             challenge: Challenge::new(),
             pub_key_cred_params: CoseAlgorithmIdentifiers::default(),
             timeout: FIVE_MINUTES,
             exclude_credentials,
             authenticator_selection: AuthenticatorSelectionCriteria::passkey(),
             hints: Hints::EMPTY,
             extensions: Extension {
                 cred_props: None,
                 cred_protect: CredProtect::UserVerificationRequired(
                     false,
                     ExtensionInfo::AllowEnforceValue,
                 ),
                 min_pin_length: None,
                 prf: None,
             },
         }
     }
     /// Deployments that want to incorporate a "something a user has" factor into a larger multi-factor
     /// authentication (MFA) setup. Specifically deployments that are _not_ userless or passwordless. It
     /// is important `exclude_credentials` contains the information for _all_ [`RegisteredCredential`]s registered
     /// to [`PublicKeyCredentialUserEntity::id`] to avoid accidentally overwriting existing credentials that
     /// have been previously registered.
     ///
     /// Creates a `PublicKeyCredentialCreationOptions` that prefers the authenticator to create a server-side
     /// credential without requiring user verification. [`Self::timeout`] is [`FIVE_MINUTES`].
     /// [`Extension::cred_props`] is [`ExtensionReq::Allow`]. [`Extension::cred_protect`] is
     /// [`CredProtect::UserVerificationOptionalWithCredentialIdList`] with `false` and
     /// [`ExtensionInfo::AllowEnforceValue`].
     ///
     /// Note some authenticators require user verification during credential registration (e.g.,
     /// [CTAP 2.0 authenticators](https://fidoalliance.org/specs/fido-v2.0-id-20180227/fido-client-to-authenticator-protocol-v2.0-id-20180227.html#authenticatorMakeCredential)).
     /// When an authenticator supports both CTAP 2.0 and
     /// [Universal 2nd Factor (U2F)](https://fidoalliance.org/specs/fido-u2f-v1.2-ps-20170411/fido-u2f-overview-v1.2-ps-20170411.html#registration-creating-a-key-pair)
     /// protocols, user agents will sometimes fall back to U2F when [`UserVerificationRequirement::Discouraged`]
     /// is requested since the latter allows for registration without user verification. If the user agent does not
     /// do this, then users will have an inconsistent experience when authenticating an already-registered
     /// credential. If this is undesirable, one can use [`UserVerificationRequirement::Required`] for this and
     /// [`PublicKeyCredentialRequestOptions::user_verification`] at the expense of requiring a user to verify
     /// themselves twice: once for the first factor and again here.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{register::{
     /// #     PublicKeyCredentialCreationOptions, PublicKeyCredentialUserEntity, UserHandle64
     /// # }, AsciiDomain, RpId};
     /// assert_eq!(
     ///     PublicKeyCredentialCreationOptions::second_factor(
     ///         &RpId::Domain(AsciiDomain::try_from("example.com".to_owned())?),
     ///         PublicKeyCredentialUserEntity {
     ///             name: "carl.gauss",
     ///             id: &UserHandle64::new(),
     ///             display_name: "Johann Carl Friedrich Gauß",
     ///         },
     ///         Vec::new()
     ///     )
     ///     .timeout
     ///     .get(),
     ///     300_000
     /// );
     /// # Ok::<_, webauthn_rp::AggErr>(())
     /// ```
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[inline]
     #[must_use]
     pub fn second_factor<'a: 'rp_id, 'b: 'user_name, 'c: 'user_display_name, 'd: 'user_id>(
         rp_id: &'a RpId,
         user: PublicKeyCredentialUserEntity<'b, 'c, 'd, USER_LEN>,
         exclude_credentials: Vec<PublicKeyCredentialDescriptor<Box<[u8]>>>,
     ) -> Self {
         let mut opts = Self::passkey(rp_id, user, exclude_credentials);
         opts.authenticator_selection = AuthenticatorSelectionCriteria::second_factor();
         opts.extensions.cred_props = Some(ExtensionReq::Allow);
         opts.extensions.cred_protect = CredProtect::UserVerificationOptionalWithCredentialIdList(
             false,
             ExtensionInfo::AllowEnforceValue,
         );
         opts
     }
 }
 /// `PublicKeyCredentialCreationOptions` based on a [`UserHandle64`].
 pub type PublicKeyCredentialCreationOptions64<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
 > = PublicKeyCredentialCreationOptions<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     USER_HANDLE_MAX_LEN,
 >;
 /// `PublicKeyCredentialCreationOptions` based on a [`UserHandle16`].
 pub type PublicKeyCredentialCreationOptions16<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
 > = PublicKeyCredentialCreationOptions<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     16,
 >;
 /// Container of a [`CredentialCreationOptions`] that has been used to start the registration ceremony.
 /// This gets sent to the client ASAP.
 #[derive(Debug)]
 pub struct RegistrationClientState<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     const USER_LEN: usize,
 >(
     CredentialCreationOptions<
         'rp_id,
         'user_name,
         'user_display_name,
         'user_id,
         'prf_first,
         'prf_second,
         USER_LEN,
     >,
 );
 impl<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     const USER_LEN: usize,
 >
     RegistrationClientState<
         'rp_id,
         'user_name,
         'user_display_name,
         'user_id,
         'prf_first,
         'prf_second,
         USER_LEN,
     >
 {
     /// Returns the `CredentialCreationOptions` that was used to start a registration ceremony.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{register::{
     /// #     CoseAlgorithmIdentifiers, CredentialCreationOptions,
     /// #     PublicKeyCredentialUserEntity, UserHandle64,
     /// # }, AsciiDomain, RpId};
     /// assert_eq!(
     ///     CredentialCreationOptions::passkey(
     ///         &RpId::Domain(AsciiDomain::try_from("example.com".to_owned())?),
     ///         PublicKeyCredentialUserEntity {
     ///             name: "david.hilbert",
     ///             id: &UserHandle64::new(),
     ///             display_name: "David Hilbert",
     ///         },
     ///         Vec::new()
     ///     )
     ///     .start_ceremony()?
     ///     .1
     ///     .options()
     ///     .public_key
     ///     .rp_id.as_ref(),
     ///     "example.com"
     /// );
     /// # Ok::<_, webauthn_rp::AggErr>(())
     /// ```
     #[inline]
     #[must_use]
     pub const fn options(
         &self,
     ) -> &CredentialCreationOptions<
         'rp_id,
         'user_name,
         'user_display_name,
         'user_id,
         'prf_first,
         'prf_second,
         USER_LEN,
     > {
         &self.0
     }
 }
 /// `RegistrationClientState` based on a [`UserHandle64`].
 pub type RegistrationClientState64<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
 > = RegistrationClientState<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     USER_HANDLE_MAX_LEN,
 >;
 /// `RegistrationClientState` based on a [`UserHandle16`].
 pub type RegistrationClientState16<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
 > = RegistrationClientState<
     'rp_id,
     'user_name,
     'user_display_name,
     'user_id,
     'prf_first,
     'prf_second,
     16,
 >;
 /// Additional verification options to perform in [`RegistrationServerState::verify`].
 #[derive(Clone, Copy, Debug)]
 pub struct RegistrationVerificationOptions<'origins, 'top_origins, O, T> {
     /// Origins to use for [origin validation](https://www.w3.org/TR/webauthn-3/#sctn-validating-origin).
     ///
     /// When this is empty, the origin that will be used will be based on
     /// the [`RpId`] passed to [`RegistrationServerState::verify`]. If [`RpId::Domain`] or [`RpId::StaticDomain`],
     /// then the [`DomainOrigin`] returned from passing [`AsciiDomain::as_ref`] and [`AsciiDomainStatic::as_str`]
     /// to [`DomainOrigin::new`] respectively will be used; otherwise the [`Url`] in [`RpId::Url`] will be used.
     pub allowed_origins: &'origins [O],
     /// [Top-level origins](https://html.spec.whatwg.org/multipage/webappapis.html#concept-environment-top-level-origin)
     /// to use for [origin validation](https://www.w3.org/TR/webauthn-3/#sctn-validating-origin).
     ///
     /// When this is `Some`, [`CollectedClientData::cross_origin`] is allowed to be `true`. When the contained
     /// `slice` is empty, [`CollectedClientData::top_origin`] must be `None`. When this is `None`,
     /// `CollectedClientData::cross_origin` must be `false` and `CollectedClientData::top_origin` must be `None`.
     pub allowed_top_origins: Option<&'top_origins [T]>,
     /// The required [`Backup`] state of the credential.
     pub backup_requirement: BackupReq,
     /// Error when unsolicited extensions are sent back iff `true`.
     pub error_on_unsolicited_extensions: bool,
     /// [`AuthenticatorAttachment`] must be sent iff `true`.
     pub require_authenticator_attachment: bool,
     /// [`CollectedClientData::from_client_data_json_relaxed`] is used to extract [`CollectedClientData`] iff `true`.
     #[cfg(feature = "serde_relaxed")]
     pub client_data_json_relaxed: bool,
 }
 impl<O, T> RegistrationVerificationOptions<'_, '_, O, T> {
     /// Returns `Self` such that [`Self::allowed_origins`] is empty, [`Self::allowed_top_origins`] is `None`,
     /// [`Self::backup_requirement`] is [`BackupReq::None`], [`Self::error_on_unsolicited_extensions`] is `true`,
     /// [`Self::require_authenticator_attachment`] is `false`, and [`Self::client_data_json_relaxed`] is
     /// `true`.
     ///
     /// Note `O` and `T` should implement `PartialEq<Origin<'_>>` (e.g., `&str`).
     #[inline]
     #[must_use]
     pub const fn new() -> Self {
         Self {
             allowed_origins: [].as_slice(),
             allowed_top_origins: None,
             backup_requirement: BackupReq::None,
             error_on_unsolicited_extensions: true,
             require_authenticator_attachment: false,
             #[cfg(feature = "serde_relaxed")]
             client_data_json_relaxed: true,
         }
     }
 }
 impl<O, T> Default for RegistrationVerificationOptions<'_, '_, O, T> {
     /// Same as [`Self::new`].
     #[inline]
     fn default() -> Self {
         Self {
             allowed_origins: &[],
             allowed_top_origins: None,
             backup_requirement: BackupReq::default(),
             error_on_unsolicited_extensions: true,
             require_authenticator_attachment: false,
             #[cfg(feature = "serde_relaxed")]
             client_data_json_relaxed: true,
         }
     }
 }
 /// `PrfInput` without the actual data sent to reduce memory usage when storing [`RegistrationServerState`] in an
 /// in-memory collection.
 #[derive(Clone, Copy, Debug)]
 enum ServerPrfInfo {
     /// No `PrfInput`.
     None,
     /// `PrfInput::second` was `None`.
     One(ExtensionInfo),
     /// `PrfInput::second` was `Some`.
     Two(ExtensionInfo),
 }
 #[cfg(test)]
 impl PartialEq for ServerPrfInfo {
     fn eq(&self, other: &Self) -> bool {
         match *self {
             Self::None => matches!(*other, Self::None),
             Self::One(info) => matches!(*other, Self::One(info2) if info == info2),
             Self::Two(info) => matches!(*other, Self::Two(info2) if info == info2),
         }
     }
 }
 impl From<Option<(PrfInput<'_, '_>, ExtensionInfo)>> for ServerPrfInfo {
     fn from(value: Option<(PrfInput<'_, '_>, ExtensionInfo)>) -> Self {
         value.map_or(Self::None, |val| {
             val.0
                 .second
                 .map_or_else(|| Self::One(val.1), |_| Self::Two(val.1))
         })
     }
 }
 /// `Extension` without the actual data sent to reduce memory usage when storing [`AuthenticationServerState`]
 /// in an in-memory collection.
 #[derive(Clone, Copy, Debug)]
 struct ServerExtensionInfo {
     /// `Extension::cred_props`.
     cred_props: Option<ExtensionReq>,
     /// `Extension::cred_protect`.
     cred_protect: CredProtect,
     /// `Extension::min_pin_length`.
     min_pin_length: Option<(FourToSixtyThree, ExtensionInfo)>,
     /// `Extension::prf`.
     prf: ServerPrfInfo,
 }
 impl ServerExtensionInfo {
     /// Validates the extensions.
     fn validate(
         self,
         client_ext: ClientExtensionsOutputs,
         auth_ext: AuthenticatorExtensionOutput,
         error_unsolicited: bool,
     ) -> Result<(), ExtensionErr> {
         if error_unsolicited {
             self.validate_unsolicited(client_ext, auth_ext)
         } else {
             Ok(())
         }
         .and_then(|()| {
             self.validate_required(client_ext, auth_ext)
                 .and_then(|()| self.validate_value(client_ext, auth_ext))
         })
     }
     /// Validates if there are any unsolicited extensions.
     ///
     /// Note no distinction is made between an extension that is empty and one that is not (i.e., we are checking
     ///  purely for the existence of extension keys).
     fn validate_unsolicited(
         mut self,
         client_ext: ClientExtensionsOutputs,
         auth_ext: AuthenticatorExtensionOutput,
     ) -> Result<(), ExtensionErr> {
         // For simpler code, we artificially set non-requested extensions after verifying there was not an error
         // and recursively call this function. There are so few extensions and the checks are fast that there
         // should be no worry of stack overflow or performance overhead.
         if self.cred_props.is_some() {
             if !matches!(self.cred_protect, CredProtect::None) {
                 if self.min_pin_length.is_some() {
                     // This is the last extension, so recursion stops here.
                     if !matches!(self.prf, ServerPrfInfo::None) {
                         Ok(())
                     } else if client_ext.prf.is_some() {
                         Err(ExtensionErr::ForbiddenPrf)
                     } else if !matches!(auth_ext.hmac_secret, HmacSecret::None) {
                         Err(ExtensionErr::ForbiddenHmacSecret)
                     } else {
                         Ok(())
                     }
                 } else if auth_ext.min_pin_length.is_some() {
                     Err(ExtensionErr::ForbiddenMinPinLength)
                 } else {
                     // Pretend to set `minPinLength`, so we can check `prf`.
                     self.min_pin_length =
                         Some((FourToSixtyThree::Four, ExtensionInfo::RequireEnforceValue));
                     self.validate_unsolicited(client_ext, auth_ext)
                 }
             } else if !matches!(auth_ext.cred_protect, CredentialProtectionPolicy::None) {
                 Err(ExtensionErr::ForbiddenCredProtect)
             } else {
                 // Pretend to set `credProtect`, so we can check `minPinLength` and `prf` extensions.
                 self.cred_protect = CredProtect::UserVerificationOptional(
                     false,
                     ExtensionInfo::RequireEnforceValue,
                 );
                 self.validate_unsolicited(client_ext, auth_ext)
             }
         } else if client_ext.cred_props.is_some() {
             Err(ExtensionErr::ForbiddenCredProps)
         } else {
             // Pretend to set `credProps`; so we can check `credProtect`, `minPinLength`, and `prf` extensions.
             self.cred_props = Some(ExtensionReq::Require);
             self.validate_unsolicited(client_ext, auth_ext)
         }
     }
     /// Validates if any required extensions don't have a corresponding response.
     ///
     /// Note empty extensions are treated as missing. For example when requiring the `credProps` extension,
     /// all of the following responses would lead to a failure:
     /// `{"clientExtensionResults":{}}`: no extensions.
     /// `{"clientExtensionResults":{"prf":true}}`: only the `prf` extension.
     /// `{"clientExtensionResults":{"credProps":{}}}`: empty `credProps` extension.
     /// `{"clientExtensionResults":{"credProps":{"foo":false}}}`: `credProps` extension doesn't contain at least one
     /// expected field (i.e., still "empty").
     fn validate_required(
         self,
         client_ext: ClientExtensionsOutputs,
         auth_ext: AuthenticatorExtensionOutput,
     ) -> Result<(), ExtensionErr> {
         // We don't check `self.cred_protect` since `CredProtect::validate` checks for both a required response
         // and value enforcement; thus it only needs to be checked once (which it is in `Self::validate_value`).
         self.cred_props
             .map_or(Ok(()), |info| {
                 if matches!(info, ExtensionReq::Require) {
                     if client_ext
                         .cred_props
                         .is_some_and(|props| props.rk.is_some())
                     {
                         Ok(())
                     } else {
                         Err(ExtensionErr::MissingCredProps)
                     }
                 } else {
                     Ok(())
                 }
             })
             .and_then(|()| {
                 self.min_pin_length
                     .map_or(Ok(()), |info| {
                         if matches!(
                             info.1,
                             ExtensionInfo::RequireEnforceValue
                                 | ExtensionInfo::RequireDontEnforceValue
                         ) {
                             auth_ext
                                 .min_pin_length
                                 .ok_or(ExtensionErr::MissingMinPinLength)
                                 .map(|_| ())
                         } else {
                             Ok(())
                         }
                     })
                     .and_then(|()| match self.prf {
                         ServerPrfInfo::None => Ok(()),
                         ServerPrfInfo::One(info) | ServerPrfInfo::Two(info) => {
                             if matches!(
                                 info,
                                 ExtensionInfo::RequireEnforceValue
                                     | ExtensionInfo::RequireDontEnforceValue
                             ) {
                                 if client_ext.prf.is_some() {
                                     Ok(())
                                 } else {
                                     Err(ExtensionErr::MissingPrf)
                                 }
                             } else {
                                 Ok(())
                             }
                         }
                     })
             })
     }
     /// Validates the value of any extensions sent from the client.
     ///
     /// Note missing and empty extensions are always OK.
     fn validate_value(
         self,
         client_ext: ClientExtensionsOutputs,
         auth_ext: AuthenticatorExtensionOutput,
     ) -> Result<(), ExtensionErr> {
         // This also checks for a missing response. Instead of duplicating that check, we only call
         // `self.cred_protect.validate` once here and not also in `Self::validate_required`.
         self.cred_protect
             .validate(auth_ext.cred_protect)
             .and_then(|()| {
                 self.min_pin_length
                     .map_or(Ok(()), |info| {
                         if matches!(
                             info.1,
                             ExtensionInfo::RequireEnforceValue | ExtensionInfo::AllowEnforceValue
                         ) {
                             auth_ext.min_pin_length.map_or(Ok(()), |pin| {
                                 if pin >= info.0 {
                                     Ok(())
                                 } else {
                                     Err(ExtensionErr::InvalidMinPinLength(info.0, pin))
                                 }
                             })
                         } else {
                             Ok(())
                         }
                     })
                     .and_then(|()| match self.prf {
                         ServerPrfInfo::None => Ok(()),
                         ServerPrfInfo::One(info) | ServerPrfInfo::Two(info) => {
                             if matches!(
                                 info,
                                 ExtensionInfo::RequireEnforceValue
                                     | ExtensionInfo::AllowEnforceValue
                             ) {
                                 client_ext
                                     .prf
                                     .map_or(Ok(()), |prf| {
                                         if prf.enabled {
                                             Ok(())
                                         } else {
                                             Err(ExtensionErr::InvalidPrfValue)
                                         }
                                     })
                                     .and({
                                         if matches!(auth_ext.hmac_secret, HmacSecret::NotEnabled) {
                                             Err(ExtensionErr::InvalidHmacSecretValue)
                                         } else {
                                             Ok(())
                                         }
                                     })
                             } else {
                                 Ok(())
                             }
                         }
                     })
             })
     }
 }
 impl From<Extension<'_, '_>> for ServerExtensionInfo {
     fn from(value: Extension<'_, '_>) -> Self {
         Self {
             cred_props: value.cred_props,
             cred_protect: value.cred_protect,
             min_pin_length: value.min_pin_length,
             prf: value.prf.into(),
         }
     }
 }
 #[cfg(test)]
 impl PartialEq for ServerExtensionInfo {
     fn eq(&self, other: &Self) -> bool {
         self.prf == other.prf
     }
 }
 // This is essentially the `PublicKeyCredentialCreationOptions` used to create it; however to reduce
 // memory usage, we remove all unnecessary data making an instance of this 48 bytes in size on
 // `x86_64-unknown-linux-gnu` platforms when `USER_LEN` is `USER_HANDLE_MIN_LEN`.
 /// State needed to be saved when beginning the registration ceremony.
 ///
 /// Saves the necessary information associated with the [`CredentialCreationOptions`] used to create it
 /// via [`CredentialCreationOptions::start_ceremony`] so that registration of a new credential can be
 /// performed with [`Self::verify`].
 ///
 /// `RegistrationServerState` implements [`Borrow`] of [`SentChallenge`]; thus to obtain the correct
 /// `RegistrationServerState` associated with a [`Registration`], one should use its corresponding
 /// [`Registration::challenge`].
 #[derive(Debug)]
 pub struct RegistrationServerState<const USER_LEN: usize> {
     /// [`mediation`](https://www.w3.org/TR/credential-management-1/#dom-credentialcreationoptions-mediation).
     mediation: CredentialMediationRequirement,
     // This is a `SentChallenge` since we need `RegistrationServerState` to be fetchable after receiving the
     // response from the client. This response must obviously be constructable; thus its challenge is a
     // `SentChallenge`.
     //
     // This must never be mutated since we want to ensure it is actually a `Challenge` (which
     // can only be constructed via `Challenge::new`). This is guaranteed to be true iff
     // `serializable_server_state` is not enabled. We avoid implementing `trait`s like `Hash` when that
     // is enabled.
     /// [`challenge`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-challenge).
     challenge: SentChallenge,
     /// [`pubKeyCredParams`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-pubkeycredparams).
     pub_key_cred_params: CoseAlgorithmIdentifiers,
     /// [`authenticatorSelection`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-authenticatorselection).
     authenticator_selection: AuthenticatorSelectionCriteria,
     /// [`extensions`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialcreationoptions-extensions).
     extensions: ServerExtensionInfo,
     /// `Instant` the ceremony expires.
     #[cfg(not(feature = "serializable_server_state"))]
     expiration: Instant,
     /// `SystemTime` the ceremony expires.
     #[cfg(feature = "serializable_server_state")]
     expiration: SystemTime,
     /// User handle.
     user_id: UserHandle<USER_LEN>,
 }
 impl<const USER_LEN: usize> RegistrationServerState<USER_LEN> {
     #[cfg(all(test, feature = "custom", feature = "serializable_server_state"))]
     fn is_eq(&self, other: &Self) -> bool {
         self.mediation == other.mediation
             && self.challenge == other.challenge
             && self.pub_key_cred_params == other.pub_key_cred_params
             && self.authenticator_selection == other.authenticator_selection
             && self.extensions == other.extensions
             && self.expiration == other.expiration
             && self.user_id == other.user_id
     }
     /// Verifies `response` is valid based on `self` consuming `self` and returning a `RegisteredCredential` that
     /// borrows the necessary data from `response`.
     ///
     /// `rp_id` MUST be the same as the [`PublicKeyCredentialCreationOptions::rp_id`] used when starting the
     /// ceremony.
     ///
     /// It is _essential_ to ensure [`RegisteredCredential::id`] has not been previously registered; if
     /// so, the ceremony SHOULD be aborted and a failure reported. When saving `RegisteredCredential`, one may
     /// want to save the [`RpId`] and [`PublicKeyCredentialUserEntity`] information; however since [`RpId`] is
     /// likely static, that may not be necessary. User information is also likely static for a given [`UserHandle`]
     /// (which is saved in `RegisteredCredential`); so if such info is saved, one may want to save it once per
     /// `UserHandle` and not per `RegisteredCredential`.
     ///
     /// # Errors
     ///
     /// Errors iff `response` is not valid according to the
     /// [registration ceremony criteria](https://www.w3.org/TR/webauthn-3/#sctn-registering-a-new-credential)
     /// or violates any of the settings in `options`.
     #[inline]
     pub fn verify<'a, O: PartialEq<Origin<'a>>, T: PartialEq<Origin<'a>>>(
         self,
         rp_id: &RpId,
         response: &'a Registration,
         options: &RegistrationVerificationOptions<'_, '_, O, T>,
     ) -> Result<RegisteredCredential<'a, USER_LEN>, RegCeremonyErr> {
         // [Registration ceremony](https://www.w3.org/TR/webauthn-3/#sctn-registering-a-new-credential)
         // is handled by:
         //
         // 1. Calling code.
         // 2. Client code and the construction of `resp` (hopefully via [`Registration::deserialize`]).
         // 3. Client code and the construction of `resp` (hopefully via [`AuthenticatorAttestation::deserialize`]).
         // 4. Client code and the construction of `resp` (hopefully via [`ClientExtensionsOutputs::deserialize`]).
         // 5. [`Self::partial_validate`].
         // 6. [`Self::partial_validate`].
         // 7. [`Self::partial_validate`].
         // 8. [`Self::partial_validate`].
         // 9. [`Self::partial_validate`].
         // 10. [`Self::partial_validate`].
         // 11. [`Self::partial_validate`].
         // 12. [`Self::partial_validate`].
         // 13. [`Self::partial_validate`].
         // 14. [`Self::partial_validate`].
         // 15. Below.
         // 16. [`Self::partial_validate`].
         // 17. [`Self::partial_validate`].
         // 18. [`Self::partial_validate`].
         // 19. [`Self::partial_validate`].
         // 20. Below.
         // 21. [`Self::partial_validate`].
         // 22. [`Self::partial_validate`].
         // 23. N/A since only none and self attestations are supported.
         // 24. Always satisfied since only none and self attestations are supported (Item 3 is N/A).
         // 25. [`Self::partial_validate`].
         // 26. Calling code.
         // 27. Below.
         // 28. N/A since only none and self attestations are supported.
         // 29. Below.
 
         // Steps 5–14, 16–19, 21–22, and 25.
         self.partial_validate(rp_id, response, (), &options.into())
             .map_err(RegCeremonyErr::from)
             .and_then(|attestation_object| {
                 let auth_data = attestation_object.auth_data();
                 let flags = auth_data.flags();
                 // Step 15.
                 if matches!(self.mediation, CredentialMediationRequirement::Conditional)
                     || flags.user_present
                 {
                     self.authenticator_selection
                         // Verify any required authenticator attachment modality.
                         .validate(
                             options.require_authenticator_attachment,
                             response.authenticator_attachment,
                         )
                         .and_then(|()| {
                             let attested_credential_data = auth_data.attested_credential_data();
                             self.pub_key_cred_params
                                 // Step 20.
                                 .validate(attested_credential_data.credential_public_key)
                                 .and_then(|()| {
                                     let extensions = auth_data.extensions();
                                     // Step 27.
                                     self.extensions
                                         .validate(
                                             response.client_extension_results,
                                             extensions,
                                             options.error_on_unsolicited_extensions,
                                         )
                                         .map_err(RegCeremonyErr::Extension)
                                         .and_then(|()| {
                                             // Step 29.
                                             RegisteredCredential::new(
                                                 attested_credential_data.credential_id,
                                                 response.response.transports(),
                                                 self.user_id,
                                                 StaticState {
                                                     credential_public_key: attested_credential_data
                                                         .credential_public_key,
                                                     extensions: extensions.into(),
                                                     client_extension_results: response
                                                         .client_extension_results
                                                         .into(),
                                                 },
                                                 DynamicState {
                                                     user_verified: flags.user_verified,
                                                     backup: flags.backup,
                                                     sign_count: auth_data.sign_count(),
                                                     authenticator_attachment: response
                                                         .authenticator_attachment,
                                                 },
                                                 Metadata {
                                                     attestation: match attestation_object
                                                         .attestation()
                                                     {
                                                         AttestationFormat::None => {
                                                             Attestation::None
                                                         }
                                                         AttestationFormat::Packed(_) => {
                                                             Attestation::Surrogate
                                                         }
                                                     },
                                                     aaguid: attested_credential_data.aaguid,
                                                     extensions: extensions.into(),
                                                     client_extension_results: response
                                                         .client_extension_results
                                                         .into(),
                                                     resident_key: self
                                                         .authenticator_selection
                                                         .resident_key,
                                                 },
                                             )
                                             .map_err(RegCeremonyErr::Credential)
                                         })
                                 })
                         })
                 } else {
                     Err(RegCeremonyErr::UserNotPresent)
                 }
             })
     }
 }
 impl<const USER_LEN: usize> TimedCeremony for RegistrationServerState<USER_LEN> {
     #[cfg(any(doc, not(feature = "serializable_server_state")))]
     #[inline]
     fn expiration(&self) -> Instant {
         self.expiration
     }
     #[cfg(all(not(doc), feature = "serializable_server_state"))]
     #[inline]
     fn expiration(&self) -> SystemTime {
         self.expiration
     }
 }
 impl<const USER_LEN: usize> Ceremony<USER_LEN, false> for RegistrationServerState<USER_LEN> {
     type R = Registration;
     fn rand_challenge(&self) -> SentChallenge {
         self.challenge
     }
     #[cfg(not(feature = "serializable_server_state"))]
     fn expiry(&self) -> Instant {
         self.expiration
     }
     #[cfg(feature = "serializable_server_state")]
     fn expiry(&self) -> SystemTime {
         self.expiration
     }
     fn user_verification(&self) -> UserVerificationRequirement {
         self.authenticator_selection.user_verification
     }
 }
 impl<const USER_LEN: usize> Borrow<SentChallenge> for RegistrationServerState<USER_LEN> {
     #[inline]
     fn borrow(&self) -> &SentChallenge {
         &self.challenge
     }
 }
 impl<const USER_LEN: usize> PartialEq for RegistrationServerState<USER_LEN> {
     #[inline]
     fn eq(&self, other: &Self) -> bool {
         self.challenge == other.challenge
     }
 }
 impl<const USER_LEN: usize> PartialEq<&Self> for RegistrationServerState<USER_LEN> {
     #[inline]
     fn eq(&self, other: &&Self) -> bool {
         *self == **other
     }
 }
 impl<const USER_LEN: usize> PartialEq<RegistrationServerState<USER_LEN>>
     for &RegistrationServerState<USER_LEN>
 {
     #[inline]
     fn eq(&self, other: &RegistrationServerState<USER_LEN>) -> bool {
         **self == *other
     }
 }
 impl<const USER_LEN: usize> Eq for RegistrationServerState<USER_LEN> {}
 impl<const USER_LEN: usize> Hash for RegistrationServerState<USER_LEN> {
     #[inline]
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.challenge.hash(state);
     }
 }
 impl<const USER_LEN: usize> PartialOrd for RegistrationServerState<USER_LEN> {
     #[inline]
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         Some(self.cmp(other))
     }
 }
 impl<const USER_LEN: usize> Ord for RegistrationServerState<USER_LEN> {
     #[inline]
     fn cmp(&self, other: &Self) -> Ordering {
         self.challenge.cmp(&other.challenge)
     }
 }
 /// `RegistrationServerState` based on a [`UserHandle64`].
 pub type RegistrationServerState64 = RegistrationServerState<USER_HANDLE_MAX_LEN>;
 /// `RegistrationServerState` based on a [`UserHandle16`].
 pub type RegistrationServerState16 = RegistrationServerState<16>;