webauthn_rp

request.rs (73243B)

---

 #[cfg(test)]
 mod tests;
 #[cfg(doc)]
 use super::{
     hash::hash_set::MaxLenHashSet,
     request::{
         auth::{
             AllowedCredential, AllowedCredentials, CredentialSpecificExtension,
             DiscoverableAuthenticationServerState, DiscoverableCredentialRequestOptions,
             NonDiscoverableAuthenticationServerState, NonDiscoverableCredentialRequestOptions,
             PublicKeyCredentialRequestOptions,
         },
         register::{CredentialCreationOptions, RegistrationServerState},
     },
     response::{AuthenticatorAttachment, register::ClientExtensionsOutputs},
 };
 use crate::{
     request::{
         error::{
             AsciiDomainErr, DomainOriginParseErr, PortParseErr, RpIdErr, SchemeParseErr, UrlErr,
         },
         register::{BackupReq, RegistrationVerificationOptions},
     },
     response::{
         AuthData as _, AuthDataContainer, AuthResponse, AuthTransports, Backup, CeremonyErr,
         CredentialId, Origin, Response, SentChallenge,
     },
 };
 use core::{
     borrow::Borrow,
     cell::Cell,
     fmt::{self, Display, Formatter},
     num::NonZeroU32,
     str::FromStr,
 };
 use rsa::sha2::{Digest as _, Sha256};
 #[cfg(any(doc, not(feature = "serializable_server_state")))]
 use std::time::Instant;
 #[cfg(feature = "serializable_server_state")]
 use std::time::SystemTime;
 use url::Url as Uri;
 /// Contains functionality for beginning the
 /// [authentication ceremony](https://www.w3.org/TR/webauthn-3/#authentication-ceremony).
 ///
 /// # Examples
 ///
 /// ```
 /// # use core::convert;
 /// # use webauthn_rp::{
 /// #     hash::hash_set::{InsertRemoveExpired, MaxLenHashSet},
 /// #     request::{
 /// #         auth::{AllowedCredentials, DiscoverableCredentialRequestOptions, NonDiscoverableCredentialRequestOptions},
 /// #         register::UserHandle64,
 /// #         Credentials, PublicKeyCredentialDescriptor, RpId,
 /// #     },
 /// #     response::{AuthTransports, CredentialId, CRED_ID_MIN_LEN},
 /// #     AggErr,
 /// # };
 /// const RP_ID: &RpId = &RpId::from_static_domain("example.com").unwrap();
 /// let mut ceremonies = MaxLenHashSet::new(128);
 /// let (server, client) = DiscoverableCredentialRequestOptions::passkey(RP_ID).start_ceremony()?;
 /// assert_eq!(ceremonies.insert_remove_all_expired(server), InsertRemoveExpired::Success);
 /// # #[cfg(feature = "custom")]
 /// let mut ceremonies_2 = MaxLenHashSet::new(128);
 /// # #[cfg(feature = "serde")]
 /// assert!(serde_json::to_string(&client).is_ok());
 /// let user_handle = get_user_handle();
 /// # #[cfg(feature = "custom")]
 /// let creds = get_registered_credentials(&user_handle)?;
 /// # #[cfg(feature = "custom")]
 /// let (server_2, client_2) =
 ///     NonDiscoverableCredentialRequestOptions::second_factor(RP_ID, creds).start_ceremony()?;
 /// # #[cfg(feature = "custom")]
 /// assert_eq!(ceremonies_2.insert_remove_all_expired(server_2), InsertRemoveExpired::Success);
 /// # #[cfg(all(feature = "custom", feature = "serde"))]
 /// assert!(serde_json::to_string(&client_2).is_ok());
 /// /// Extract `UserHandle` from session cookie.
 /// fn get_user_handle() -> UserHandle64 {
 ///     // ⋮
 /// #     UserHandle64::new()
 /// }
 /// # #[cfg(feature = "custom")]
 /// /// Fetch the `AllowedCredentials` associated with `user`.
 /// fn get_registered_credentials(user: &UserHandle64) -> Result<AllowedCredentials, AggErr> {
 ///     // ⋮
 /// #     let mut creds = AllowedCredentials::new();
 /// #     creds.push(
 /// #         PublicKeyCredentialDescriptor {
 /// #             id: CredentialId::try_from(vec![0; CRED_ID_MIN_LEN].into_boxed_slice())?,
 /// #             transports: AuthTransports::NONE,
 /// #         }
 /// #         .into(),
 /// #     );
 /// #     Ok(creds)
 /// }
 /// # Ok::<_, AggErr>(())
 /// ```
 pub mod auth;
 /// Contains error types.
 pub mod error;
 /// Contains functionality for beginning the
 /// [registration ceremony](https://www.w3.org/TR/webauthn-3/#registration-ceremony).
 ///
 /// # Examples
 ///
 /// ```
 /// # use core::convert;
 /// # use webauthn_rp::{
 /// #     hash::hash_set::{InsertRemoveExpired, MaxLenHashSet},
 /// #     request::{
 /// #         register::{
 /// #             CredentialCreationOptions, PublicKeyCredentialUserEntity, UserHandle, USER_HANDLE_MAX_LEN, UserHandle64,
 /// #         },
 /// #         PublicKeyCredentialDescriptor, RpId
 /// #     },
 /// #     response::{AuthTransports, CredentialId, CRED_ID_MIN_LEN},
 /// #     AggErr,
 /// # };
 /// const RP_ID: &RpId = &RpId::from_static_domain("example.com").unwrap();
 /// # #[cfg(feature = "custom")]
 /// let mut ceremonies = MaxLenHashSet::new(128);
 /// # #[cfg(feature = "custom")]
 /// let user_handle = get_user_handle();
 /// # #[cfg(feature = "custom")]
 /// let user = get_user_entity(&user_handle)?;
 /// # #[cfg(feature = "custom")]
 /// let creds = get_registered_credentials(&user_handle)?;
 /// # #[cfg(feature = "custom")]
 /// let (server, client) = CredentialCreationOptions::passkey(RP_ID, user.clone(), creds)
 ///     .start_ceremony()?;
 /// # #[cfg(feature = "custom")]
 /// assert_eq!(ceremonies.insert_remove_all_expired(server), InsertRemoveExpired::Success);
 /// # #[cfg(all(feature = "serde", feature = "custom"))]
 /// assert!(serde_json::to_string(&client).is_ok());
 /// # #[cfg(feature = "custom")]
 /// let creds_2 = get_registered_credentials(&user_handle)?;
 /// # #[cfg(feature = "custom")]
 /// let (server_2, client_2) =
 ///     CredentialCreationOptions::second_factor(RP_ID, user, creds_2).start_ceremony()?;
 /// # #[cfg(feature = "custom")]
 /// assert_eq!(ceremonies.insert_remove_all_expired(server_2), InsertRemoveExpired::Success);
 /// # #[cfg(all(feature = "serde", feature = "custom"))]
 /// assert!(serde_json::to_string(&client_2).is_ok());
 /// /// Extract `UserHandle` from session cookie or storage if this is not the first credential registered.
 /// # #[cfg(feature = "custom")]
 /// fn get_user_handle() -> UserHandle64 {
 ///     // ⋮
 /// #     [0; USER_HANDLE_MAX_LEN].into()
 /// }
 /// /// Fetch `PublicKeyCredentialUserEntity` info associated with `user`.
 /// ///
 /// /// If this is the first time a credential is being registered, then `PublicKeyCredentialUserEntity`
 /// /// will need to be constructed with `name` and `display_name` passed from the client and `UserHandle::new`
 /// /// used for `id`. Once created, this info can be stored such that the entity information
 /// /// does not need to be requested for subsequent registrations.
 /// # #[cfg(feature = "custom")]
 /// fn get_user_entity(user: &UserHandle64) -> Result<PublicKeyCredentialUserEntity<'_, '_, '_, USER_HANDLE_MAX_LEN>, AggErr> {
 ///     // ⋮
 /// #     Ok(PublicKeyCredentialUserEntity {
 /// #         name: "foo",
 /// #         id: user,
 /// #         display_name: "",
 /// #     })
 /// }
 /// /// Fetch the `PublicKeyCredentialDescriptor`s associated with `user`.
 /// ///
 /// /// This doesn't need to be called when this is the first credential registered for `user`; instead
 /// /// an empty `Vec` should be passed.
 /// fn get_registered_credentials(
 ///     user: &UserHandle64,
 /// ) -> Result<Vec<PublicKeyCredentialDescriptor<Box<[u8]>>>, AggErr> {
 ///     // ⋮
 /// #     Ok(Vec::new())
 /// }
 /// # Ok::<_, AggErr>(())
 /// ```
 pub mod register;
 /// Contains functionality to serialize data to a client.
 #[cfg(feature = "serde")]
 mod ser;
 /// Contains functionality to (de)serialize data needed for [`RegistrationServerState`],
 /// [`DiscoverableAuthenticationServerState`], and [`NonDiscoverableAuthenticationServerState`] to a data store.
 #[cfg(feature = "serializable_server_state")]
 pub(super) mod ser_server_state;
 // `Challenge` must _never_ be constructable directly or indirectly; thus its tuple field must always be private,
 // and it must never implement `trait`s (e.g., `Clone`) that would allow indirect creation. It must only ever
 // be constructed via `Self::new` or `Self::default`. In contrast downstream code must be able to construct
 // `SentChallenge` since it is used during ceremony validation; thus we must keep `Challenge` and `SentChallenge`
 // as separate types.
 /// [Cryptographic challenge](https://www.w3.org/TR/webauthn-3/#sctn-cryptographic-challenges).
 #[expect(
     missing_copy_implementations,
     reason = "want to enforce randomly-generated challenges"
 )]
 #[derive(Debug)]
 pub struct Challenge(u128);
 impl Challenge {
     /// The number of bytes a `Challenge` takes to encode in base64url.
     pub(super) const BASE64_LEN: usize = base64url_nopad::encode_len(16);
     /// Generates a random `Challenge`.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Challenge;
     /// // The probability of a `Challenge` being 0 (assuming a good entropy
     /// // source) is 2^-128 ≈ 2.9 x 10^-39.
     /// assert_ne!(Challenge::new().into_data(), 0);
     /// ```
     #[inline]
     #[must_use]
     pub fn new() -> Self {
         Self(rand::random())
     }
     /// Returns the contained `u128` consuming `self`.
     #[inline]
     #[must_use]
     pub const fn into_data(self) -> u128 {
         self.0
     }
     /// Returns the contained `u128`.
     #[inline]
     #[must_use]
     pub const fn as_data(&self) -> u128 {
         self.0
     }
     /// Returns the contained `u128` as a little-endian `array` consuming `self`.
     #[inline]
     #[must_use]
     pub const fn into_array(self) -> [u8; 16] {
         self.as_array()
     }
     /// Returns the contained `u128` as a little-endian `array`.
     #[expect(
         clippy::little_endian_bytes,
         reason = "Challenge and SentChallenge need to be compatible, and we need to ensure the data is sent and received in the same order"
     )]
     #[inline]
     #[must_use]
     pub const fn as_array(&self) -> [u8; 16] {
         self.0.to_le_bytes()
     }
 }
 impl Default for Challenge {
     /// Same as [`Self::new`].
     #[inline]
     fn default() -> Self {
         Self::new()
     }
 }
 impl From<Challenge> for u128 {
     #[inline]
     fn from(value: Challenge) -> Self {
         value.0
     }
 }
 impl From<&Challenge> for u128 {
     #[inline]
     fn from(value: &Challenge) -> Self {
         value.0
     }
 }
 impl From<Challenge> for [u8; 16] {
     #[inline]
     fn from(value: Challenge) -> Self {
         value.into_array()
     }
 }
 impl From<&Challenge> for [u8; 16] {
     #[inline]
     fn from(value: &Challenge) -> Self {
         value.as_array()
     }
 }
 /// A [domain](https://url.spec.whatwg.org/#concept-domain) in representation format consisting of only and any
 /// ASCII.
 ///
 /// The only ASCII character disallowed in a label is `'.'` since it is used exclusively as a separator. Every
 /// label must have length inclusively between 1 and 63, and the total length of the domain must be at most 253
 /// when a trailing `'.'` does not exist; otherwise the max length is 254. The root domain (i.e., `'.'`) is not
 /// allowed.
 ///
 /// Note if the domain is a `&'static str`, then use [`AsciiDomainStatic`] instead.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct AsciiDomain(String);
 impl AsciiDomain {
     /// Removes a trailing `'.'` if it exists.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{AsciiDomain, error::AsciiDomainErr};
     /// let mut dom = AsciiDomain::try_from("example.com.".to_owned())?;
     /// assert_eq!(dom.as_ref(), "example.com.");
     /// dom.remove_trailing_dot();
     /// assert_eq!(dom.as_ref(), "example.com");
     /// dom.remove_trailing_dot();
     /// assert_eq!(dom.as_ref(), "example.com");
     /// # Ok::<_, AsciiDomainErr>(())
     /// ```
     #[expect(clippy::unreachable, reason = "want to crash when there is a bug")]
     #[inline]
     pub fn remove_trailing_dot(&mut self) {
         if *self
             .0
             .as_bytes()
             .last()
             .unwrap_or_else(|| unreachable!("there is a bug in AsciiDomain::from_slice"))
             == b'.'
         {
             _ = self.0.pop();
         }
     }
 }
 impl AsRef<str> for AsciiDomain {
     #[inline]
     fn as_ref(&self) -> &str {
         self.0.as_str()
     }
 }
 impl Borrow<str> for AsciiDomain {
     #[inline]
     fn borrow(&self) -> &str {
         self.0.as_str()
     }
 }
 impl From<AsciiDomain> for String {
     #[inline]
     fn from(value: AsciiDomain) -> Self {
         value.0
     }
 }
 impl PartialEq<&Self> for AsciiDomain {
     #[inline]
     fn eq(&self, other: &&Self) -> bool {
         *self == **other
     }
 }
 impl PartialEq<AsciiDomain> for &AsciiDomain {
     #[inline]
     fn eq(&self, other: &AsciiDomain) -> bool {
         **self == *other
     }
 }
 impl TryFrom<Vec<u8>> for AsciiDomain {
     type Error = AsciiDomainErr;
     /// Verifies `value` is an ASCII domain in representation format converting any uppercase ASCII into
     /// lowercase.
     ///
     /// Note it is _strongly_ encouraged for `value` to only contain letters, numbers, hyphens, and underscores;
     /// otherwise certain applications may consider it not a domain. If the original domain contains non-ASCII, then
     /// one must encode it in Punycode _before_ calling this function. Domains that have a trailing `'.'` will be
     /// considered differently than domains without it; thus one will likely want to trim it if it does exist
     /// (e.g., [`AsciiDomain::remove_trailing_dot`]). Because this allows any ASCII, one may want to ensure `value`
     /// is not an IP address.
     ///
     /// # Errors
     ///
     /// Errors iff `value` is not a valid ASCII domain.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{error::AsciiDomainErr, AsciiDomain};
     /// // Root `'.'` is not removed if it exists.
     /// assert_ne!("example.com", AsciiDomain::try_from(b"example.com.".to_vec())?.as_ref());
     /// // Root domain (i.e., `'.'`) is not allowed.
     /// assert!(AsciiDomain::try_from(vec![b'.']).is_err());
     /// // Uppercase is transformed into lowercase.
     /// assert_eq!("example.com", AsciiDomain::try_from(b"ExAmPle.CoM".to_vec())?.as_ref());
     /// // The only ASCII character not allowed in a domain label is `'.'` as it is used exclusively to delimit
     /// // labels.
     /// assert_eq!("\x00", AsciiDomain::try_from(b"\x00".to_vec())?.as_ref());
     /// // Empty labels are not allowed.
     /// assert!(AsciiDomain::try_from(b"example..com".to_vec()).is_err());
     /// // Labels cannot have length greater than 63.
     /// let mut long_label = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa".to_owned();
     /// assert_eq!(long_label.len(), 64);
     /// assert!(AsciiDomain::try_from(long_label.clone().into_bytes()).is_err());
     /// long_label.pop();
     /// assert_eq!(long_label, AsciiDomain::try_from(long_label.clone().into_bytes())?.as_ref());
     /// // The maximum length of a domain is 254 if a trailing `'.'` exists; otherwise the max length is 253.
     /// let mut long_domain = format!("{long_label}.{long_label}.{long_label}.{long_label}");
     /// long_domain.pop();
     /// long_domain.push('.');
     /// assert_eq!(long_domain.len(), 255);
     /// assert!(AsciiDomain::try_from(long_domain.clone().into_bytes()).is_err());
     /// long_domain.pop();
     /// long_domain.pop();
     /// long_domain.push('.');
     /// assert_eq!(long_domain.len(), 254);
     /// assert_eq!(long_domain, AsciiDomain::try_from(long_domain.clone().into_bytes())?.as_ref());
     /// long_domain.pop();
     /// long_domain.push('a');
     /// assert_eq!(long_domain.len(), 254);
     /// assert!(AsciiDomain::try_from(long_domain.clone().into_bytes()).is_err());
     /// long_domain.pop();
     /// assert_eq!(long_domain.len(), 253);
     /// assert_eq!(long_domain, AsciiDomain::try_from(long_domain.clone().into_bytes())?.as_ref());
     /// // Only ASCII is allowed; thus if a domain needs to be Punycode-encoded, then it must be _before_ calling
     /// // this function.
     /// assert!(AsciiDomain::try_from("λ.com".to_owned().into_bytes()).is_err());
     /// assert_eq!("xn--wxa.com", AsciiDomain::try_from(b"xn--wxa.com".to_vec())?.as_ref());
     /// # Ok::<_, AsciiDomainErr>(())
     /// ```
     #[expect(unsafe_code, reason = "comment justifies correctness")]
     #[expect(
         clippy::arithmetic_side_effects,
         reason = "comments justify correctness"
     )]
     #[inline]
     fn try_from(mut value: Vec<u8>) -> Result<Self, Self::Error> {
         /// Value to add to an uppercase ASCII `u8` to get the lowercase version.
         const DIFF: u8 = b'a' - b'A';
         let bytes = value.as_slice();
         bytes
             .as_ref()
             .last()
             .ok_or(AsciiDomainErr::Empty)
             .and_then(|b| {
                 let len = bytes.len();
                 if *b == b'.' {
                     if len == 1 {
                         Err(AsciiDomainErr::RootDomain)
                     } else if len > 254 {
                         Err(AsciiDomainErr::Len)
                     } else {
                         Ok(())
                     }
                 } else if len > 253 {
                     Err(AsciiDomainErr::Len)
                 } else {
                     Ok(())
                 }
             })
             .and_then(|()| {
                 value
                     .iter_mut()
                     .try_fold(0u8, |mut label_len, byt| {
                         let b = *byt;
                         if b == b'.' {
                             if label_len == 0 {
                                 Err(AsciiDomainErr::EmptyLabel)
                             } else {
                                 Ok(0)
                             }
                         } else if label_len == 63 {
                             Err(AsciiDomainErr::LabelLen)
                         } else {
                             // We know `label_len` is less than 63, thus this won't overflow.
                             label_len += 1;
                             match b {
                                 // Non-uppercase ASCII is allowed and doesn't need to be converted.
                                 ..b'A' | b'['..=0x7F => Ok(label_len),
                                 // Uppercase ASCII is allowed but needs to be transformed into lowercase.
                                 b'A'..=b'Z' => {
                                     // Lowercase ASCII is a contiguous block starting from `b'a'` as is uppercase
                                     // ASCII which starts from `b'A'` with uppercase ASCII coming before; thus we
                                     // simply need to shift by a fixed amount.
                                     *byt += DIFF;
                                     Ok(label_len)
                                 }
                                 // Non-ASCII is disallowed.
                                 0x80.. => Err(AsciiDomainErr::NotAscii),
                             }
                         }
                     })
                     .map(|_| {
                         // SAFETY:
                         // We just verified `value` only contains ASCII; thus this is safe.
                         let utf8 = unsafe { String::from_utf8_unchecked(value) };
                         Self(utf8)
                     })
             })
     }
 }
 impl TryFrom<String> for AsciiDomain {
     type Error = AsciiDomainErr;
     /// Same as [`Self::try_from`] except `value` is a `String`.
     #[inline]
     fn try_from(value: String) -> Result<Self, Self::Error> {
         Self::try_from(value.into_bytes())
     }
 }
 /// Similar to [`AsciiDomain`] except the contained data is a `&'static str`.
 ///
 /// Since [`Self::new`] and [`Option::unwrap`] are `const fn`s, one can define a global `const` or `static`
 /// variable that represents the RP ID.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct AsciiDomainStatic(&'static str);
 impl AsciiDomainStatic {
     /// Returns the contained `str`.
     #[inline]
     #[must_use]
     pub const fn as_str(self) -> &'static str {
         self.0
     }
     /// Verifies `domain` is a valid lowercase ASCII domain returning `None` when not valid or when
     /// uppercase ASCII exists.
     ///
     /// Read [`AsciiDomain`] for more information about what constitutes a valid domain.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{AsciiDomainStatic, RpId};
     /// /// RP ID of our application.
     /// const RP_IP: &RpId = &RpId::StaticDomain(AsciiDomainStatic::new("example.com").unwrap());
     /// ```
     #[expect(
         clippy::arithmetic_side_effects,
         reason = "comment justifies correctness"
     )]
     #[expect(
         clippy::else_if_without_else,
         reason = "part of if branch and else branch are the same"
     )]
     #[inline]
     #[must_use]
     pub const fn new(domain: &'static str) -> Option<Self> {
         let mut utf8 = domain.as_bytes();
         if let Some(lst) = utf8.last() {
             let len = utf8.len();
             if *lst == b'.' {
                 if len == 1 || len > 254 {
                     return None;
                 }
             } else if len > 253 {
                 return None;
             }
             let mut label_len = 0;
             while let [first, ref rest @ ..] = *utf8 {
                 if first == b'.' {
                     if label_len == 0 {
                         return None;
                     }
                     label_len = 0;
                 } else if label_len == 63 {
                     return None;
                 } else {
                     match first {
                         // Any non-uppercase ASCII is allowed.
                         // We know `label_len` is less than 63, so this won't overflow.
                         ..b'A' | b'['..=0x7F => label_len += 1,
                         // Uppercase ASCII and non-ASCII are disallowed.
                         b'A'..=b'Z' | 0x80.. => return None,
                     }
                 }
                 utf8 = rest;
             }
             Some(Self(domain))
         } else {
             None
         }
     }
 }
 impl AsRef<str> for AsciiDomainStatic {
     #[inline]
     fn as_ref(&self) -> &str {
         self.as_str()
     }
 }
 impl Borrow<str> for AsciiDomainStatic {
     #[inline]
     fn borrow(&self) -> &str {
         self.as_str()
     }
 }
 impl From<AsciiDomainStatic> for &'static str {
     #[inline]
     fn from(value: AsciiDomainStatic) -> Self {
         value.0
     }
 }
 impl From<AsciiDomainStatic> for String {
     #[inline]
     fn from(value: AsciiDomainStatic) -> Self {
         value.0.to_owned()
     }
 }
 impl From<AsciiDomainStatic> for AsciiDomain {
     #[inline]
     fn from(value: AsciiDomainStatic) -> Self {
         Self(value.0.to_owned())
     }
 }
 impl PartialEq<&Self> for AsciiDomainStatic {
     #[inline]
     fn eq(&self, other: &&Self) -> bool {
         *self == **other
     }
 }
 impl PartialEq<AsciiDomainStatic> for &AsciiDomainStatic {
     #[inline]
     fn eq(&self, other: &AsciiDomainStatic) -> bool {
         **self == *other
     }
 }
 /// The output of the [URL serializer](https://url.spec.whatwg.org/#concept-url-serializer).
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Url(String);
 impl AsRef<str> for Url {
     #[inline]
     fn as_ref(&self) -> &str {
         self.0.as_str()
     }
 }
 impl Borrow<str> for Url {
     #[inline]
     fn borrow(&self) -> &str {
         self.0.as_str()
     }
 }
 impl From<Url> for String {
     #[inline]
     fn from(value: Url) -> Self {
         value.0
     }
 }
 impl PartialEq<&Self> for Url {
     #[inline]
     fn eq(&self, other: &&Self) -> bool {
         *self == **other
     }
 }
 impl PartialEq<Url> for &Url {
     #[inline]
     fn eq(&self, other: &Url) -> bool {
         **self == *other
     }
 }
 impl FromStr for Url {
     type Err = UrlErr;
     #[inline]
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         let violation = Cell::new(false);
         Uri::options()
             .syntax_violation_callback(Some(&|_| {
                 violation.set(true);
             }))
             .parse(s)
             .map_err(|_e| UrlErr)
             .and_then(|url| {
                 if violation.into_inner() {
                     Err(UrlErr)
                 } else {
                     Ok(Self(url.into()))
                 }
             })
     }
 }
 /// [RP ID](https://w3c.github.io/webauthn/#rp-id).
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum RpId {
     /// An ASCII domain.
     ///
     /// Note web platforms MUST use this variant; and if possible, non-web platforms should too. Also despite
     /// the spec currently requiring RP IDs to be
     /// [valid domain strings](https://url.spec.whatwg.org/#valid-domain-string), this is unnecessarily strict
     /// and will likely be relaxed in a [future version](https://github.com/w3c/webauthn/issues/2206); thus
     /// any ASCII domain is allowed.
     Domain(AsciiDomain),
     /// Similar to [`Self::Domain`] except the ASCII domain is static.
     ///
     /// Since [`AsciiDomainStatic::new`] is a `const fn`, one can define a `const` or `static` global variable
     /// the contains the RP ID.
     StaticDomain(AsciiDomainStatic),
     /// A URL.
     Url(Url),
 }
 impl RpId {
     /// Returns `Some` containing an [`AsciiDomainStatic`] iff [`AsciiDomainStatic::new`] does.
     #[inline]
     #[must_use]
     pub const fn from_static_domain(domain: &'static str) -> Option<Self> {
         if let Some(dom) = AsciiDomainStatic::new(domain) {
             Some(Self::StaticDomain(dom))
         } else {
             None
         }
     }
     /// Validates `hash` is the same as the SHA-256 hash of `self`.
     fn validate_rp_id_hash<E>(&self, hash: &[u8]) -> Result<(), CeremonyErr<E>> {
         if *hash == *Sha256::digest(self.as_ref()) {
             Ok(())
         } else {
             Err(CeremonyErr::RpIdHashMismatch)
         }
     }
 }
 impl AsRef<str> for RpId {
     #[inline]
     fn as_ref(&self) -> &str {
         match *self {
             Self::Domain(ref dom) => dom.as_ref(),
             Self::StaticDomain(dom) => dom.as_str(),
             Self::Url(ref url) => url.as_ref(),
         }
     }
 }
 impl Borrow<str> for RpId {
     #[inline]
     fn borrow(&self) -> &str {
         match *self {
             Self::Domain(ref dom) => dom.borrow(),
             Self::StaticDomain(dom) => dom.as_str(),
             Self::Url(ref url) => url.borrow(),
         }
     }
 }
 impl From<RpId> for String {
     #[inline]
     fn from(value: RpId) -> Self {
         match value {
             RpId::Domain(dom) => dom.into(),
             RpId::StaticDomain(dom) => dom.into(),
             RpId::Url(url) => url.into(),
         }
     }
 }
 impl PartialEq<&Self> for RpId {
     #[inline]
     fn eq(&self, other: &&Self) -> bool {
         *self == **other
     }
 }
 impl PartialEq<RpId> for &RpId {
     #[inline]
     fn eq(&self, other: &RpId) -> bool {
         **self == *other
     }
 }
 impl From<AsciiDomain> for RpId {
     #[inline]
     fn from(value: AsciiDomain) -> Self {
         Self::Domain(value)
     }
 }
 impl From<AsciiDomainStatic> for RpId {
     #[inline]
     fn from(value: AsciiDomainStatic) -> Self {
         Self::StaticDomain(value)
     }
 }
 impl From<Url> for RpId {
     #[inline]
     fn from(value: Url) -> Self {
         Self::Url(value)
     }
 }
 impl TryFrom<String> for RpId {
     type Error = RpIdErr;
     /// Returns `Ok` iff `value` is a valid [`Url`] or [`AsciiDomain`].
     ///
     /// Note when `value` is a valid `Url` and `AsciiDomain`, it will be treated as a `Url`.
     #[inline]
     fn try_from(value: String) -> Result<Self, Self::Error> {
         Url::from_str(value.as_str())
             .map(Self::Url)
             .or_else(|_err| {
                 AsciiDomain::try_from(value)
                     .map(Self::Domain)
                     .map_err(|_e| RpIdErr)
             })
     }
 }
 /// A URI scheme. This can be used to make
 /// [origin validation](https://www.w3.org/TR/webauthn-3/#sctn-validating-origin) more convenient.
 #[derive(Clone, Copy, Debug, Default)]
 pub enum Scheme<'a> {
     /// A scheme must not exist when validating the origin.
     None,
     /// Any scheme, or no scheme at all, is allowed to exist when validating the origin.
     Any,
     /// The HTTPS scheme must exist when validating the origin.
     #[default]
     Https,
     /// The SSH scheme must exist when validating the origin.
     Ssh,
     /// The contained `str` scheme must exist when validating the origin.
     Other(&'a str),
     /// [`Self::None`] or [`Self::Https`].
     NoneHttps,
     /// [`Self::None`] or [`Self::Ssh`].
     NoneSsh,
     /// [`Self::None`] or [`Self::Other`].
     NoneOther(&'a str),
 }
 impl Scheme<'_> {
     /// `self` is any `Scheme`; however `other` is assumed to only be a `Scheme` from a `DomainOrigin` returned
     /// from `DomainOrigin::try_from`. The latter implies that `other` is only `Scheme::None`, `Scheme::Https`,
     /// `Scheme::Ssh`, or `Scheme::Other`; furthermore when `Scheme::Other`, it won't contain a `str` that is
     /// empty or equal to "https" or "ssh".
     #[expect(clippy::unreachable, reason = "there is a bug, so we want to crash")]
     fn is_equal_to_origin_scheme(self, other: Self) -> bool {
         match self {
             Self::None => matches!(other, Self::None),
             Self::Any => true,
             Self::Https => matches!(other, Self::Https),
             Self::Ssh => matches!(other, Self::Ssh),
             Self::Other(scheme) => match other {
                 Self::None => false,
                 // We want to crash and burn since there is a bug in code.
                 Self::Any | Self::NoneHttps | Self::NoneSsh | Self::NoneOther(_) => {
                     unreachable!("there is a bug in DomainOrigin::try_from")
                 }
                 Self::Https => scheme == "https",
                 Self::Ssh => scheme == "ssh",
                 Self::Other(scheme_other) => scheme == scheme_other,
             },
             Self::NoneHttps => match other {
                 Self::None | Self::Https => true,
                 Self::Ssh | Self::Other(_) => false,
                 // We want to crash and burn since there is a bug in code.
                 Self::Any | Self::NoneHttps | Self::NoneSsh | Self::NoneOther(_) => {
                     unreachable!("there is a bug in DomainOrigin::try_from")
                 }
             },
             Self::NoneSsh => match other {
                 Self::None | Self::Ssh => true,
                 // We want to crash and burn since there is a bug in code.
                 Self::Any | Self::NoneHttps | Self::NoneSsh | Self::NoneOther(_) => {
                     unreachable!("there is a bug in DomainOrigin::try_from")
                 }
                 Self::Https | Self::Other(_) => false,
             },
             Self::NoneOther(scheme) => match other {
                 Self::None => true,
                 // We want to crash and burn since there is a bug in code.
                 Self::Any | Self::NoneHttps | Self::NoneSsh | Self::NoneOther(_) => {
                     unreachable!("there is a bug in DomainOrigin::try_from")
                 }
                 Self::Https => scheme == "https",
                 Self::Ssh => scheme == "ssh",
                 Self::Other(scheme_other) => scheme == scheme_other,
             },
         }
     }
 }
 impl<'a: 'b, 'b> TryFrom<&'a str> for Scheme<'b> {
     type Error = SchemeParseErr;
     /// `"https"` and `"ssh"` get mapped to [`Self::Https`] and [`Self::Ssh`] respectively. All other
     /// values get mapped to [`Self::Other`].
     ///
     /// # Errors
     ///
     /// Errors iff `s` is empty.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Scheme;
     /// assert!(matches!(Scheme::try_from("https")?, Scheme::Https));
     /// assert!(matches!(Scheme::try_from("https ")?, Scheme::Other(scheme) if scheme == "https "));
     /// assert!(matches!(Scheme::try_from("ssh")?, Scheme::Ssh));
     /// assert!(matches!(Scheme::try_from("Ssh")?, Scheme::Other(scheme) if scheme == "Ssh"));
     /// // Even though one can construct an empty `Scheme` via `Scheme::Other` or `Scheme::NoneOther`,
     /// // one cannot parse one.
     /// assert!(Scheme::try_from("").is_err());
     /// # Ok::<_, webauthn_rp::AggErr>(())
     /// ```
     #[inline]
     fn try_from(value: &'a str) -> Result<Self, Self::Error> {
         match value {
             "" => Err(SchemeParseErr),
             "https" => Ok(Self::Https),
             "ssh" => Ok(Self::Ssh),
             _ => Ok(Self::Other(value)),
         }
     }
 }
 /// A TCP/UDP port. This can be used to make
 /// [origin validation](https://www.w3.org/TR/webauthn-3/#sctn-validating-origin) more convenient.
 #[derive(Clone, Copy, Debug, Default)]
 pub enum Port {
     /// A port must not exist when validating the origin.
     #[default]
     None,
     /// Any port, or no port at all, is allowed to exist when validating the origin.
     Any,
     /// The contained `u16` port must exist when validating the origin.
     Val(u16),
     /// [`Self::None`] or [`Self::Val`].
     NoneVal(u16),
 }
 impl Port {
     /// `self` is any `Port`; however `other` is assumed to only be a `Port` from a `DomainOrigin` returned
     /// from `DomainOrigin::try_from`. The latter implies that `other` is only `Port::None` or `Port::Val`.
     #[expect(clippy::unreachable, reason = "there is a bug, so we want to crash")]
     fn is_equal_to_origin_port(self, other: Self) -> bool {
         match self {
             Self::None => matches!(other, Self::None),
             Self::Any => true,
             Self::Val(port) => match other {
                 Self::None => false,
                 // There is a bug in code so we want to crash and burn.
                 Self::Any | Self::NoneVal(_) => {
                     unreachable!("there is a bug in DomainOrigin::try_from")
                 }
                 Self::Val(port_other) => port == port_other,
             },
             Self::NoneVal(port) => match other {
                 Self::None => true,
                 // There is a bug in code so we want to crash and burn.
                 Self::Any | Self::NoneVal(_) => {
                     unreachable!("there is a bug in DomainOrigin::try_from")
                 }
                 Self::Val(port_other) => port == port_other,
             },
         }
     }
 }
 impl FromStr for Port {
     type Err = PortParseErr;
     /// Parses `s` as a 16-bit unsigned integer without leading 0s returning [`Self::Val`] with the contained
     /// `u16`.
     ///
     /// # Errors
     ///
     /// Errors iff `s` is not a valid 16-bit unsigned integer in decimal notation without leading 0s.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{error::PortParseErr, Port};
     /// assert!(matches!("443".parse()?, Port::Val(443)));
     /// // TCP/UDP ports have to be in canonical form:
     /// assert!("022"
     ///     .parse::<Port>()
     ///     .map_or_else(|err| matches!(err, PortParseErr::NotCanonical), |_| false));
     /// # Ok::<_, webauthn_rp::AggErr>(())
     /// ```
     #[inline]
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         s.parse().map_err(PortParseErr::ParseInt).and_then(|port| {
             if s.len()
                 == match port {
                     ..=9 => 1,
                     10..=99 => 2,
                     100..=999 => 3,
                     1_000..=9_999 => 4,
                     10_000.. => 5,
                 }
             {
                 Ok(Self::Val(port))
             } else {
                 Err(PortParseErr::NotCanonical)
             }
         })
     }
 }
 /// A [`tuple origin`](https://html.spec.whatwg.org/multipage/browsers.html#concept-origin-tuple).
 ///
 /// This can be used to make [origin validation](https://www.w3.org/TR/webauthn-3/#sctn-validating-origin)
 /// more convenient.
 #[derive(Clone, Copy, Debug)]
 pub struct DomainOrigin<'a, 'b> {
     /// The scheme.
     pub scheme: Scheme<'a>,
     /// The host.
     pub host: &'b str,
     /// The TCP/UDP port.
     pub port: Port,
 }
 impl<'b> DomainOrigin<'_, 'b> {
     /// Returns a `DomainOrigin` with [`Self::scheme`] as [`Scheme::Https`], [`Self::host`] as `host`, and
     /// [`Self::port`] as [`Port::None`].
     ///
     /// # Examples
     ///
     /// ```
     /// # extern crate alloc;
     /// # use alloc::borrow::Cow;
     /// # use webauthn_rp::{request::DomainOrigin, response::Origin};
     /// assert_eq!(
     ///     DomainOrigin::new("www.example.com"),
     ///     Origin(Cow::Borrowed("https://www.example.com"))
     /// );
     /// // `DomainOrigin::new` does not allow _any_ port to exist.
     /// assert_ne!(
     ///     DomainOrigin::new("www.example.com"),
     ///     Origin(Cow::Borrowed("https://www.example.com:443"))
     /// );
     /// ```
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[must_use]
     #[inline]
     pub const fn new<'c: 'b>(host: &'c str) -> Self {
         Self {
             scheme: Scheme::Https,
             host,
             port: Port::None,
         }
     }
     /// Returns a `DomainOrigin` with [`Self::scheme`] as [`Scheme::Https`], [`Self::host`] as `host`, and
     /// [`Self::port`] as [`Port::Any`].
     ///
     /// # Examples
     ///
     /// ```
     /// # extern crate alloc;
     /// # use alloc::borrow::Cow;
     /// # use webauthn_rp::{request::DomainOrigin, response::Origin};
     /// // Any port is allowed to exist.
     /// assert_eq!(
     ///     DomainOrigin::new_ignore_port("www.example.com"),
     ///     Origin(Cow::Borrowed("https://www.example.com:1234"))
     /// );
     /// // A port doesn't have to exist at all either.
     /// assert_eq!(
     ///     DomainOrigin::new_ignore_port("www.example.com"),
     ///     Origin(Cow::Borrowed("https://www.example.com"))
     /// );
     /// ```
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[must_use]
     #[inline]
     pub const fn new_ignore_port<'c: 'b>(host: &'c str) -> Self {
         Self {
             scheme: Scheme::Https,
             host,
             port: Port::Any,
         }
     }
 }
 impl PartialEq<Origin<'_>> for DomainOrigin<'_, '_> {
     /// Returns `true` iff [`DomainOrigin::scheme`], [`DomainOrigin::host`], and [`DomainOrigin::port`] are the
     /// same after calling [`DomainOrigin::try_from`] on `other.0.as_str()`.
     ///
     /// Note that [`Scheme`] and [`Port`] need not be the same variant. For example [`Scheme::Https`] and
     /// [`Scheme::Other`] containing `"https"` will be treated the same.
     #[inline]
     fn eq(&self, other: &Origin<'_>) -> bool {
         DomainOrigin::try_from(other.0.as_ref()).is_ok_and(|dom| {
             self.scheme.is_equal_to_origin_scheme(dom.scheme)
                 && self.host == dom.host
                 && self.port.is_equal_to_origin_port(dom.port)
         })
     }
 }
 impl PartialEq<Origin<'_>> for &DomainOrigin<'_, '_> {
     #[inline]
     fn eq(&self, other: &Origin<'_>) -> bool {
         **self == *other
     }
 }
 impl PartialEq<&Origin<'_>> for DomainOrigin<'_, '_> {
     #[inline]
     fn eq(&self, other: &&Origin<'_>) -> bool {
         *self == **other
     }
 }
 impl PartialEq<DomainOrigin<'_, '_>> for Origin<'_> {
     #[inline]
     fn eq(&self, other: &DomainOrigin<'_, '_>) -> bool {
         *other == *self
     }
 }
 impl PartialEq<DomainOrigin<'_, '_>> for &Origin<'_> {
     #[inline]
     fn eq(&self, other: &DomainOrigin<'_, '_>) -> bool {
         *other == **self
     }
 }
 impl PartialEq<&DomainOrigin<'_, '_>> for Origin<'_> {
     #[inline]
     fn eq(&self, other: &&DomainOrigin<'_, '_>) -> bool {
         **other == *self
     }
 }
 impl<'a: 'b + 'c, 'b, 'c> TryFrom<&'a str> for DomainOrigin<'b, 'c> {
     type Error = DomainOriginParseErr;
     /// `value` is parsed according to the following extended regex:
     ///
     /// `^([^:]*:\/\/)?[^:]*(:.*)?$`
     ///
     /// where the `[^:]*` of the first capturing group is parsed according to [`Scheme::try_from`], and
     /// the `.*` of the second capturing group is parsed according to [`Port::from_str`].
     ///
     /// # Errors
     ///
     /// Errors iff `Scheme::try_from` or `Port::from_str` fail when applicable.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{DomainOrigin, Port, Scheme};
     /// assert!(
     ///     DomainOrigin::try_from("https://www.example.com:443").map_or(false, |dom| matches!(
     ///         dom.scheme,
     ///         Scheme::Https
     ///     ) && dom.host
     ///         == "www.example.com"
     ///         && matches!(dom.port, Port::Val(port) if port == 443))
     /// );
     /// // Parsing is done in a case sensitive way.
     /// assert!(DomainOrigin::try_from("Https://www.EXample.com").map_or(
     ///     false,
     ///     |dom| matches!(dom.scheme, Scheme::Other(scheme) if scheme == "Https")
     ///         && dom.host == "www.EXample.com"
     ///         && matches!(dom.port, Port::None)
     /// ));
     /// ```
     #[inline]
     fn try_from(value: &'a str) -> Result<Self, Self::Error> {
         // Any string that contains `':'` is not a [valid domain](https://url.spec.whatwg.org/#valid-domain), and
         // and `"//"` never exists in a `Port`; thus if `"://"` exists, it's either invalid or delimits the scheme
         // from the rest of the origin.
         match value.split_once("://") {
             None => Ok((Scheme::None, value)),
             Some((poss_scheme, rem)) => Scheme::try_from(poss_scheme)
                 .map_err(DomainOriginParseErr::Scheme)
                 .map(|scheme| (scheme, rem)),
         }
         .and_then(|(scheme, rem)| {
             // `':'` never exists in a valid domain; thus if it exists, it's either invalid or
             // separates the domain from the port.
             rem.split_once(':')
                 .map_or_else(
                     || Ok((rem, Port::None)),
                     |(rem2, poss_port)| {
                         Port::from_str(poss_port)
                             .map_err(DomainOriginParseErr::Port)
                             .map(|port| (rem2, port))
                     },
                 )
                 .map(|(host, port)| Self { scheme, host, port })
         })
     }
 }
 /// [`PublicKeyCredentialDescriptor`](https://www.w3.org/TR/webauthn-3/#dictdef-publickeycredentialdescriptor)
 /// associated with a registered credential.
 #[derive(Clone, Debug)]
 pub struct PublicKeyCredentialDescriptor<T> {
     /// [`id`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialdescriptor-id).
     pub id: CredentialId<T>,
     /// [`transports`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialdescriptor-transports).
     pub transports: AuthTransports,
 }
 /// [`UserVerificationRequirement`](https://www.w3.org/TR/webauthn-3/#enumdef-userverificationrequirement).
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum UserVerificationRequirement {
     /// [`required`](https://www.w3.org/TR/webauthn-3/#dom-userverificationrequirement-required).
     Required,
     /// [`discouraged`](https://www.w3.org/TR/webauthn-3/#dom-userverificationrequirement-discouraged).
     ///
     /// Note some authenticators always require user verification when registering a credential (e.g.,
     /// [CTAP 2.0](https://fidoalliance.org/specs/fido-v2.0-ps-20190130/fido-client-to-authenticator-protocol-v2.0-ps-20190130.html)
     /// authenticators that have had a PIN enabled).
     Discouraged,
     /// [`preferred`](https://www.w3.org/TR/webauthn-3/#dom-userverificationrequirement-preferred).
     Preferred,
 }
 /// [`PublicKeyCredentialHint`](https://www.w3.org/TR/webauthn-3/#enumdef-publickeycredentialhint).
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum PublicKeyCredentialHint {
     /// [`security-key`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialhint-security-key).
     SecurityKey,
     /// [`client-device`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialhint-client-device).
     ClientDevice,
     /// [`hybrid`](https://www.w3.org/TR/webauthn-3/#dom-publickeycredentialhint-hybrid).
     Hybrid,
 }
 impl PublicKeyCredentialHint {
     /// Returns `true` iff `self` is the same as `other`.
     const fn is_eq(self, other: Self) -> bool {
         match self {
             Self::SecurityKey => matches!(other, Self::SecurityKey),
             Self::ClientDevice => matches!(other, Self::ClientDevice),
             Self::Hybrid => matches!(other, Self::Hybrid),
         }
     }
 }
 /// Unique sequence of [`PublicKeyCredentialHint`].
 #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
 pub struct Hints([Option<PublicKeyCredentialHint>; 3]);
 impl Hints {
     /// Empty sequence of [`PublicKeyCredentialHint`]s.
     pub const EMPTY: Self = Self([None; 3]);
     /// Adds `hint` to `self` iff `self` doesn't already contain `hint`.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{Hints, PublicKeyCredentialHint};
     /// assert_eq!(
     ///     Hints::EMPTY
     ///         .add(PublicKeyCredentialHint::SecurityKey)
     ///         .first(),
     ///     Some(PublicKeyCredentialHint::SecurityKey)
     /// );
     /// ```
     #[inline]
     #[must_use]
     pub const fn add(mut self, hint: PublicKeyCredentialHint) -> Self {
         let mut vals = self.0.as_mut_slice();
         while let [ref mut first, ref mut rem @ ..] = *vals {
             match *first {
                 None => {
                     *first = Some(hint);
                     return self;
                 }
                 Some(h) => {
                     if h.is_eq(hint) {
                         return self;
                     }
                 }
             }
             vals = rem;
         }
         self
     }
     /// Returns the first `PublicKeyCredentialHint`.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Hints;
     /// assert!(Hints::EMPTY.first().is_none());
     /// ```
     #[inline]
     #[must_use]
     pub const fn first(self) -> Option<PublicKeyCredentialHint> {
         self.0[0]
     }
     /// Returns the second `PublicKeyCredentialHint`.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Hints;
     /// assert!(Hints::EMPTY.second().is_none());
     /// ```
     #[inline]
     #[must_use]
     pub const fn second(self) -> Option<PublicKeyCredentialHint> {
         self.0[1]
     }
     /// Returns the third `PublicKeyCredentialHint`.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Hints;
     /// assert!(Hints::EMPTY.third().is_none());
     /// ```
     #[inline]
     #[must_use]
     pub const fn third(self) -> Option<PublicKeyCredentialHint> {
         self.0[2]
     }
     /// Returns the number of [`PublicKeyCredentialHint`]s in `self`.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Hints;
     /// assert_eq!(Hints::EMPTY.count(), 0);
     /// ```
     #[expect(
         clippy::arithmetic_side_effects,
         clippy::as_conversions,
         reason = "comment justifies correctness"
     )]
     #[inline]
     #[must_use]
     pub const fn count(self) -> u8 {
         // `bool as u8` is well-defined. This maxes at 3, so overflow isn't possible.
         self.first().is_some() as u8 + self.second().is_some() as u8 + self.third().is_some() as u8
     }
     /// Returns `true` iff `self` is empty.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Hints;
     /// assert!(Hints::EMPTY.is_empty());
     /// ```
     #[inline]
     #[must_use]
     pub const fn is_empty(self) -> bool {
         self.count() == 0
     }
     /// Returns `true` iff `self` contains `hint`.
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::{Hints, PublicKeyCredentialHint};
     /// assert!(!Hints::EMPTY.contains(PublicKeyCredentialHint::Hybrid));
     /// ```
     #[inline]
     #[must_use]
     pub const fn contains(self, hint: PublicKeyCredentialHint) -> bool {
         let mut vals = self.0.as_slice();
         while let [ref first, ref rem @ ..] = *vals {
             match *first {
                 None => return false,
                 Some(h) => {
                     if h.is_eq(hint) {
                         return true;
                     }
                 }
             }
             vals = rem;
         }
         false
     }
     /// Returns `true` iff `self` contains a `hint` that maps to [`AuthenticatorAttachment::CrossPlatform`].
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Hints;
     /// assert!(!Hints::EMPTY.contains_platform_hints());
     /// ```
     #[inline]
     #[must_use]
     pub const fn contains_cross_platform_hints(self) -> bool {
         let mut vals = self.0.as_slice();
         while let [ref first, ref rem @ ..] = *vals {
             match *first {
                 None => return false,
                 Some(h) => {
                     if matches!(
                         h,
                         PublicKeyCredentialHint::SecurityKey | PublicKeyCredentialHint::Hybrid
                     ) {
                         return true;
                     }
                 }
             }
             vals = rem;
         }
         false
     }
     /// Returns `true` iff `self` contains a `hint` that maps to [`AuthenticatorAttachment::Platform`].
     ///
     /// # Examples
     ///
     /// ```
     /// # use webauthn_rp::request::Hints;
     /// assert!(!Hints::EMPTY.contains_platform_hints());
     /// ```
     #[inline]
     #[must_use]
     pub const fn contains_platform_hints(self) -> bool {
         let mut vals = self.0.as_slice();
         while let [ref first, ref rem @ ..] = *vals {
             match *first {
                 None => return false,
                 Some(h) => {
                     if h.is_eq(PublicKeyCredentialHint::ClientDevice) {
                         return true;
                     }
                 }
             }
             vals = rem;
         }
         false
     }
 }
 /// Controls if the response to a requested extension is required to be sent back.
 ///
 /// Note when requiring an extension, the extension must not only be sent back but also
 /// contain at least one expected field (e.g., [`ClientExtensionsOutputs::cred_props`] must be
 /// `Some(CredentialPropertiesOutput { rk: Some(_) })`.
 ///
 /// If one wants to additionally control the values of an extension, use [`ExtensionInfo`].
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum ExtensionReq {
     /// The response to a requested extension is required to be sent back.
     Require,
     /// The response to a requested extension is allowed, but not required, to be sent back.
     Allow,
 }
 /// Dictates how an extension should be processed.
 ///
 /// If one wants to only control if the extension should be returned, use [`ExtensionReq`].
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum ExtensionInfo {
     /// Require the associated extension and enforce its value.
     RequireEnforceValue,
     /// Require the associated extension but don't enforce its value.
     RequireDontEnforceValue,
     /// Allow the associated extension to exist and enforce its value when it does exist.
     AllowEnforceValue,
     /// Allow the associated extension to exist but don't enforce its value.
     AllowDontEnforceValue,
 }
 impl Display for ExtensionInfo {
     #[inline]
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.write_str(match *self {
             Self::RequireEnforceValue => "require the corresponding extension response and enforce its value",
             Self::RequireDontEnforceValue => "require the corresponding extension response but don't enforce its value",
             Self::AllowEnforceValue => "don't require the corresponding extension response; but if sent, enforce its value",
             Self::AllowDontEnforceValue => "don't require the corresponding extension response; and if sent, don't enforce its value",
         })
     }
 }
 /// [`CredentialMediationRequirement`](https://www.w3.org/TR/credential-management-1/#enumdef-credentialmediationrequirement).
 ///
 /// Note [`silent`](https://www.w3.org/TR/credential-management-1/#dom-credentialmediationrequirement-silent)
 /// is not supported for WebAuthn credentials, and
 /// [`optional`](https://www.w3.org/TR/credential-management-1/#dom-credentialmediationrequirement-optional)
 /// is just an alias for [`Self::Required`].
 #[expect(clippy::doc_markdown, reason = "false positive")]
 #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
 pub enum CredentialMediationRequirement {
     /// [`required`](https://www.w3.org/TR/credential-management-1/#dom-credentialmediationrequirement-required).
     ///
     /// This is the default mediation for ceremonies.
     #[default]
     Required,
     /// [`conditional`](https://www.w3.org/TR/credential-management-1/#dom-credentialmediationrequirement-conditional).
     ///
     /// Note that when registering a new credential with [`CredentialCreationOptions::mediation`] set to
     /// `Self::Conditional`, [`UserVerificationRequirement::Required`] MUST NOT be used unless user verification
     /// can be explicitly performed during the ceremony.
     Conditional,
 }
 /// A container of "credentials".
 ///
 /// This is mainly a way to unify [`Vec`] of [`PublicKeyCredentialDescriptor`]
 /// and [`AllowedCredentials`]. This can be useful in situations when one only
 /// deals with [`AllowedCredential`]s with empty [`CredentialSpecificExtension`]s
 /// essentially making them the same as [`PublicKeyCredentialDescriptor`]s.
 ///
 /// # Examples
 ///
 /// ```
 /// # use webauthn_rp::{
 /// #     request::{
 /// #         auth::AllowedCredentials, register::UserHandle, Credentials, PublicKeyCredentialDescriptor,
 /// #     },
 /// #     response::{AuthTransports, CredentialId},
 /// # };
 /// /// Fetches all credentials under `user_handle` to be allowed during authentication for non-discoverable
 /// /// requests.
 /// # #[cfg(feature = "custom")]
 /// fn get_allowed_credentials<const LEN: usize>(user_handle: &UserHandle<LEN>) -> AllowedCredentials {
 ///     get_credentials(user_handle)
 /// }
 /// /// Fetches all credentials under `user_handle` to be excluded during registration.
 /// # #[cfg(feature = "custom")]
 /// fn get_excluded_credentials<const LEN: usize>(
 ///     user_handle: &UserHandle<LEN>,
 /// ) -> Vec<PublicKeyCredentialDescriptor<Box<[u8]>>> {
 ///     get_credentials(user_handle)
 /// }
 /// /// Used to fetch the excluded `PublicKeyCredentialDescriptor`s associated with `user_handle` during
 /// /// registration as well as the `AllowedCredentials` containing `AllowedCredential`s with no credential-specific
 /// /// extensions which is used for non-discoverable requests.
 /// # #[cfg(feature = "custom")]
 /// fn get_credentials<const LEN: usize, T>(user_handle: &UserHandle<LEN>) -> T
 /// where
 ///     T: Credentials,
 ///     PublicKeyCredentialDescriptor<Box<[u8]>>: Into<T::Credential>,
 /// {
 ///     let iter = get_cred_parts(user_handle);
 ///     let len = iter.size_hint().0;
 ///     iter.fold(T::with_capacity(len), |mut creds, parts| {
 ///         creds.push(
 ///             PublicKeyCredentialDescriptor {
 ///                 id: parts.0,
 ///                 transports: parts.1,
 ///             }
 ///             .into(),
 ///         );
 ///         creds
 ///     })
 /// }
 /// /// Fetches all `CredentialId`s and associated `AuthTransports` under `user_handle`
 /// /// from the database.
 /// # #[cfg(feature = "custom")]
 /// fn get_cred_parts<const LEN: usize>(
 ///     user_handle: &UserHandle<LEN>,
 /// ) -> impl Iterator<Item = (CredentialId<Box<[u8]>>, AuthTransports)> {
 ///     // ⋮
 /// #     [(
 /// #         CredentialId::try_from(vec![0; 16].into_boxed_slice()).unwrap(),
 /// #         AuthTransports::NONE,
 /// #     )]
 /// #     .into_iter()
 /// }
 /// ```
 pub trait Credentials: Sized {
     /// The "credential"s that make up `Self`.
     type Credential;
     /// Returns `Self`.
     #[inline]
     #[must_use]
     fn new() -> Self {
         Self::with_capacity(0)
     }
     /// Returns `Self` with at least `capacity` allocated.
     fn with_capacity(capacity: usize) -> Self;
     /// Adds `cred` to `self`.
     ///
     /// Returns `true` iff `cred` was added.
     fn push(&mut self, cred: Self::Credential) -> bool;
     /// Returns the number of [`Self::Credential`]s in `Self`.
     fn len(&self) -> usize;
     /// Returns `true` iff [`Self::len`] is `0`.
     #[inline]
     fn is_empty(&self) -> bool {
         self.len() == 0
     }
 }
 impl<T> Credentials for Vec<T> {
     type Credential = T;
     #[inline]
     fn with_capacity(capacity: usize) -> Self {
         Self::with_capacity(capacity)
     }
     #[inline]
     fn push(&mut self, cred: Self::Credential) -> bool {
         self.push(cred);
         true
     }
     #[inline]
     fn len(&self) -> usize {
         self.len()
     }
 }
 /// Additional options that control how [`Ceremony::partial_validate`] works.
 struct CeremonyOptions<'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`], then the [`DomainOrigin`] returned from
     /// passing [`AsciiDomain::as_ref`] to [`DomainOrigin::new`] will be used; otherwise the [`Url`] in
     /// [`RpId::Url`] will be used.
     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`.
     allowed_top_origins: Option<&'top_origins [T]>,
     /// The required [`Backup`] state of the credential.
     backup_requirement: BackupReq,
     /// [`CollectedClientData::from_client_data_json_relaxed`] is used to extract [`CollectedClientData`] iff `true`.
     #[cfg(feature = "serde_relaxed")]
     client_data_json_relaxed: bool,
 }
 impl<'o, 't, O, T> From<&RegistrationVerificationOptions<'o, 't, O, T>>
     for CeremonyOptions<'o, 't, O, T>
 {
     fn from(value: &RegistrationVerificationOptions<'o, 't, O, T>) -> Self {
         Self {
             allowed_origins: value.allowed_origins,
             allowed_top_origins: value.allowed_top_origins,
             backup_requirement: value.backup_requirement,
             #[cfg(feature = "serde_relaxed")]
             client_data_json_relaxed: value.client_data_json_relaxed,
         }
     }
 }
 /// Functionality common to both registration and authentication ceremonies.
 ///
 /// Designed to be implemented on the _request_ side.
 trait Ceremony<const USER_LEN: usize, const DISCOVERABLE: bool> {
     /// The type of response that is associated with the ceremony.
     type R: Response;
     /// Challenge.
     fn rand_challenge(&self) -> SentChallenge;
     /// `Instant` the ceremony was expires.
     #[cfg(not(feature = "serializable_server_state"))]
     fn expiry(&self) -> Instant;
     /// `Instant` the ceremony was expires.
     #[cfg(feature = "serializable_server_state")]
     fn expiry(&self) -> SystemTime;
     /// User verification requirement.
     fn user_verification(&self) -> UserVerificationRequirement;
     /// Performs validation of ceremony criteria common to both ceremony types.
     #[expect(
         clippy::type_complexity,
         reason = "type aliases with bounds are even more problematic at least until lazy_type_alias is stable"
     )]
     #[expect(clippy::too_many_lines, reason = "102 lines is fine")]
     fn partial_validate<'a, O: PartialEq<Origin<'a>>, T: PartialEq<Origin<'a>>>(
         &self,
         rp_id: &RpId,
         resp: &'a Self::R,
         key: <<Self::R as Response>::Auth as AuthResponse>::CredKey<'_>,
         options: &CeremonyOptions<'_, '_, O, T>,
     ) -> Result<
         <<Self::R as Response>::Auth as AuthResponse>::Auth<'a>,
         CeremonyErr<
             <<<Self::R as Response>::Auth as AuthResponse>::Auth<'a> as AuthDataContainer<'a>>::Err,
         >,
     > {
         // [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. Below via [`CollectedClientData::from_client_data_json_relaxed`].
         // 6. Below via [`CollectedClientData::from_client_data_json_relaxed`] or [`CollectedClientData::from_client_data_json_relaxed`].
         // 7. Below via [`CollectedClientData::from_client_data_json_relaxed`] or [`CollectedClientData::from_client_data_json_relaxed`].
         // 8. Below.
         // 9. Below.
         // 10. Below.
         // 11. Below.
         // 12. Below via [`AuthenticatorAttestation::new`].
         // 13. Below via [`AttestationObject::parse_data`].
         // 14. Below.
         // 15. [`RegistrationServerState::verify`].
         // 16. Below.
         // 17. Below via [`AuthenticatorData::from_cbor`].
         // 18. Below.
         // 19. Below.
         // 20. [`RegistrationServerState::verify`].
         // 21. Below via [`AttestationObject::parse_data`].
         // 22. Below via [`AttestationObject::parse_data`].
         // 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. Below via [`AttestedCredentialData::from_cbor`].
         // 26. Calling code.
         // 27. [`RegistrationServerState::verify`].
         // 28. N/A since only none and self attestations are supported.
         // 29. [`RegistrationServerState::verify`].
         //
         //
         // [Authentication ceremony](https://www.w3.org/TR/webauthn-3/#sctn-verifying-assertion)
         // is handled by:
         //
         // 1. Calling code.
         // 2. Client code and the construction of `resp` (hopefully via [`Authentication::deserialize`]).
         // 3. Client code and the construction of `resp` (hopefully via [`AuthenticatorAssertion::deserialize`]).
         // 4. Client code and the construction of `resp` (hopefully via [`ClientExtensionsOutputs::deserialize`]).
         // 5. [`AuthenticationServerState::verify`].
         // 6. [`AuthenticationServerState::verify`].
         // 7. Informative only in that it defines variables.
         // 8. Below via [`CollectedClientData::from_client_data_json_relaxed`].
         // 9. Below via [`CollectedClientData::from_client_data_json_relaxed`] or [`CollectedClientData::from_client_data_json_relaxed`].
         // 10. Below via [`CollectedClientData::from_client_data_json_relaxed`] or [`CollectedClientData::from_client_data_json_relaxed`].
         // 11. Below.
         // 12. Below.
         // 13. Below.
         // 14. Below.
         // 15. Below.
         // 16. Below via [`AuthenticatorData::from_cbor`].
         // 17. Below.
         // 18. Below via [`AuthenticatorData::from_cbor`].
         // 19. Below.
         // 20. Below via [`AuthenticatorAssertion::new`].
         // 21. Below.
         // 22. [`AuthenticationServerState::verify`].
         // 23. [`AuthenticationServerState::verify`].
         // 24. [`AuthenticationServerState::verify`].
         // 25. [`AuthenticationServerState::verify`].
 
         // Enforce timeout.
         #[cfg(not(feature = "serializable_server_state"))]
         let active = self.expiry() >= Instant::now();
         #[cfg(feature = "serializable_server_state")]
         let active = self.expiry() >= SystemTime::now();
         if active {
             #[cfg(feature = "serde_relaxed")]
             let relaxed = options.client_data_json_relaxed;
             #[cfg(not(feature = "serde_relaxed"))]
             let relaxed = false;
             resp.auth()
                 // Steps 5–7, 12–13, 17, 21–22, and 25 of the registration ceremony.
                 // Steps 8–10, 16, 18, and 20–21 of the authentication ceremony.
                 .parse_data_and_verify_sig(key, relaxed)
                 .map_err(CeremonyErr::AuthResp)
                 .and_then(|(client_data_json, auth_response)| {
                     if options.allowed_origins.is_empty() {
                         if match *rp_id {
                             RpId::Domain(ref dom) => {
                                 // Steps 9 and 12 of the registration and authentication ceremonies
                                 // respectively.
                                 DomainOrigin::new(dom.as_ref()) == client_data_json.origin
                             }
                             // Steps 9 and 12 of the registration and authentication ceremonies
                             // respectively.
                             RpId::Url(ref url) => url == client_data_json.origin,
                             RpId::StaticDomain(dom) => {
                                 DomainOrigin::new(dom.0) == client_data_json.origin
                             }
                         } {
                             Ok(())
                         } else {
                             Err(CeremonyErr::OriginMismatch)
                         }
                     } else {
                         options
                             .allowed_origins
                             .iter()
                             // Steps 9 and 12 of the registration and authentication ceremonies
                             // respectively.
                             .find(|o| **o == client_data_json.origin)
                             .ok_or(CeremonyErr::OriginMismatch)
                             .map(|_| ())
                     }
                     .and_then(|()| {
                         // Steps 10–11 of the registration ceremony.
                         // Steps 13–14 of the authentication ceremony.
                         match options.allowed_top_origins {
                             None => {
                                 if client_data_json.cross_origin {
                                     Err(CeremonyErr::CrossOrigin)
                                 } else if client_data_json.top_origin.is_some() {
                                     Err(CeremonyErr::TopOriginMismatch)
                                 } else {
                                     Ok(())
                                 }
                             }
                             Some(top_origins) => client_data_json.top_origin.map_or(Ok(()), |t| {
                                 top_origins
                                     .iter()
                                     .find(|top| **top == t)
                                     .ok_or(CeremonyErr::TopOriginMismatch)
                                     .map(|_| ())
                             }),
                         }
                         .and_then(|()| {
                             // Steps 8 and 11 of the registration and authentication ceremonies
                             // respectively.
                             if self.rand_challenge() == client_data_json.challenge {
                                 let auth_data = auth_response.authenticator_data();
                                 rp_id
                                     // Steps 14 and 15 of the registration and authentication ceremonies
                                     // respectively.
                                     .validate_rp_id_hash(auth_data.rp_hash())
                                     .and_then(|()| {
                                         let flag = auth_data.flag();
                                         // Steps 16 and 17 of the registration and authentication ceremonies
                                         // respectively.
                                         if flag.user_verified
                                             || !matches!(
                                                 self.user_verification(),
                                                 UserVerificationRequirement::Required
                                             )
                                         {
                                             // Steps 18–19 of the registration ceremony.
                                             // Step 19 of the authentication ceremony.
                                             match options.backup_requirement {
                                                 BackupReq::None => Ok(()),
                                                 BackupReq::NotEligible => {
                                                     if matches!(flag.backup, Backup::NotEligible) {
                                                         Ok(())
                                                     } else {
                                                         Err(CeremonyErr::BackupEligible)
                                                     }
                                                 }
                                                 BackupReq::Eligible => {
                                                     if matches!(flag.backup, Backup::NotEligible) {
                                                         Err(CeremonyErr::BackupNotEligible)
                                                     } else {
                                                         Ok(())
                                                     }
                                                 }
                                                 BackupReq::EligibleNotExists => {
                                                     if matches!(flag.backup, Backup::Eligible) {
                                                         Ok(())
                                                     } else {
                                                         Err(CeremonyErr::BackupExists)
                                                     }
                                                 }
                                                 BackupReq::Exists => {
                                                     if matches!(flag.backup, Backup::Exists) {
                                                         Ok(())
                                                     } else {
                                                         Err(CeremonyErr::BackupDoesNotExist)
                                                     }
                                                 }
                                             }
                                         } else {
                                             Err(CeremonyErr::UserNotVerified)
                                         }
                                     })
                                     .map(|()| auth_response)
                             } else {
                                 Err(CeremonyErr::ChallengeMismatch)
                             }
                         })
                     })
                 })
         } else {
             Err(CeremonyErr::Timeout)
         }
     }
 }
 /// "Ceremonies" stored on the server that expire after a certain duration.
 ///
 /// Types like [`RegistrationServerState`] and [`DiscoverableAuthenticationServerState`] are based on [`Challenge`]s
 /// that expire after a certain duration.
 pub trait TimedCeremony {
     /// Returns the `Instant` the ceremony expires.
     ///
     /// Note when `serializable_server_state` is enabled, [`SystemTime`] is returned instead.
     #[cfg_attr(docsrs, doc(auto_cfg = false))]
     #[cfg(any(doc, not(feature = "serializable_server_state")))]
     fn expiration(&self) -> Instant;
     /// Returns the `SystemTime` the ceremony expires.
     #[cfg(all(not(doc), feature = "serializable_server_state"))]
     fn expiration(&self) -> SystemTime;
 }
 /// [`AuthenticationExtensionsPRFValues`](https://www.w3.org/TR/webauthn-3/#dictdef-authenticationextensionsprfvalues).
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct PrfInput<'first, 'second> {
     /// [`first`](https://www.w3.org/TR/webauthn-3/#dom-authenticationextensionsprfvalues-first).
     pub first: &'first [u8],
     /// [`second`](https://www.w3.org/TR/webauthn-3/#dom-authenticationextensionsprfvalues-second).
     pub second: Option<&'second [u8]>,
 }
 impl<'first, 'second> PrfInput<'first, 'second> {
     /// Returns a `PrfInput` with [`Self::first`] set to `first` and [`Self::second`] set to `None`.
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[inline]
     #[must_use]
     pub const fn with_first<'a: 'first>(first: &'a [u8]) -> Self {
         Self {
             first,
             second: None,
         }
     }
     /// Same as [`Self::with_first`] except [`Self::second`] is set to `Some` containing `second`.
     #[expect(single_use_lifetimes, reason = "false positive")]
     #[inline]
     #[must_use]
     pub const fn with_two<'a: 'first, 'b: 'second>(first: &'a [u8], second: &'b [u8]) -> Self {
         Self {
             first,
             second: Some(second),
         }
     }
 }
 /// The number of milliseconds in 5 minutes.
 ///
 /// This is the recommended default timeout duration for ceremonies
 /// [in the spec](https://www.w3.org/TR/webauthn-3/#sctn-timeout-recommended-range).
 pub const FIVE_MINUTES: NonZeroU32 = NonZeroU32::new(300_000).unwrap();