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use serde::{Serialize, Deserialize};
use rand::{Rng, distributions::Alphanumeric};
use sha2::{Sha256, Digest};
use data_encoding::BASE64URL;
/// Methods to use for PKCE challenges.
#[derive(PartialEq, Eq, Copy, Clone, Debug, Serialize, Deserialize, /*Default*/)]
pub enum PKCEMethod {
/// Base64-encoded SHA256 hash of an ASCII string.
//#[default]
S256,
/// Plain string by itself. Please don't use this.
#[serde(rename = "snake_case")]
Plain
}
// manual impl until Rust 1.62 hits nixos-unstable
impl Default for PKCEMethod {
fn default() -> Self { PKCEMethod::S256 }
}
impl PKCEMethod {
/// Return a string representing a PKCE method as it would be serialized.
pub fn as_str(&self) -> &'static str {
match self {
PKCEMethod::S256 => "S256",
PKCEMethod::Plain => "plain"
}
}
}
/// A PKCE verifier string that should be kept in secret until the end
/// of the authentication ceremony, where it is revealed to prove that
/// the one who uses the grant is the same entity who it was given to.
#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
pub struct PKCEVerifier(pub(super) String);
impl AsRef<str> for PKCEVerifier {
fn as_ref(&self) -> &str {
self.0.as_str()
}
}
impl ToString for PKCEVerifier {
fn to_string(&self) -> String {
self.0.clone()
}
}
impl PKCEVerifier {
/// Generate a new PKCE verifier string of 128 bytes in length.
#[allow(clippy::new_without_default)]
pub fn new() -> Self {
let bytes = rand::thread_rng()
.sample_iter(&Alphanumeric)
.take(128)
.collect::<Vec<u8>>();
Self(String::from_utf8(bytes).unwrap())
}
}
/// A PKCE challenge as described in [RFC7636].
///
/// [RFC7636]: https://tools.ietf.org/html/rfc7636
#[derive(Eq, PartialEq, Debug, Clone, Serialize, Deserialize)]
pub struct PKCEChallenge {
code_challenge: String,
#[serde(rename = "code_challenge_method")]
method: PKCEMethod
}
impl PKCEChallenge {
/// Create a new challenge from a [PKCEVerifier] using a certain
/// [PKCEMethod].
pub fn new(code_verifier: PKCEVerifier, method: PKCEMethod) -> Self {
Self {
code_challenge: match method {
PKCEMethod::S256 => {
let mut hasher = Sha256::new();
hasher.update(code_verifier.as_ref());
BASE64URL.encode(&hasher.finalize())
},
PKCEMethod::Plain => code_verifier.to_string(),
},
method
}
}
/// Verify that the [PKCEVerifier] corresponds to this challenge,
/// by creating a second challenge string and comparing it against
/// this challenge data.
///
/// ```rust
/// use kittybox_indieauth::{PKCEVerifier, PKCEMethod, PKCEChallenge};
///
/// let verifier = PKCEVerifier::new();
/// let challenge = PKCEChallenge::new(verifier.clone(), PKCEMethod::default());
/// // Meanwhile, at the token endpoint, in the end of the ceremony...
/// // ...the challenge gets retrieved from the stored data and verified
/// assert!(challenge.verify(verifier))
/// ```
#[must_use]
pub fn verify(&self, code_verifier: PKCEVerifier) -> bool {
Self::new(code_verifier, self.method) == *self
}
/// Return a reference to the code challenge string.
pub fn as_str(&self) -> &str {
self.code_challenge.as_str()
}
/// Return the method used to create this challenge.
pub fn method(&self) -> PKCEMethod {
self.method
}
}
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