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|
use serde::{Serialize, Deserialize};
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
}
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<T: Into<String>> From<T> for PKCEVerifier {
fn from(t: T) -> Self {
Self(t.into())
}
}
impl AsRef<str> for PKCEVerifier {
fn as_ref(&self) -> &str {
self.0.as_str()
}
}
// We don't need Display here, this is not a user-facing value.
#[allow(clippy::to_string_trait_impl)]
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 {
Self::from_rng(&mut rand::thread_rng())
}
/// Generate a new PKCE string of 128 bytes in length, using
/// the provided random number generator.
pub fn from_rng(rng: &mut (impl rand::CryptoRng + rand::Rng)) -> Self {
use rand::{Rng, distributions::Alphanumeric};
let bytes = 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());
let mut challenge = BASE64URL.encode(&hasher.finalize());
// Trim padding
challenge.retain(|c| c != '=');
challenge
},
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, 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
}
}
#[cfg(test)]
mod tests {
use super::{PKCEMethod, PKCEVerifier, PKCEChallenge};
#[test]
/// A snapshot test generated using [Aaron Parecki's PKCE
/// tools](https://example-app.com/pkce) that checks for a
/// conforming challenge.
fn test_pkce_challenge_verification() {
let verifier = PKCEVerifier("ec03310e4e90f7bc988af05384060c3c1afeae4bb4d0f648c5c06b63".to_owned());
let challenge = PKCEChallenge::new(&verifier, PKCEMethod::S256);
assert_eq!(challenge.as_str(), "aB8OG20Rh8UoQ9gFhI0YvPkx4dDW2MBspBKGXL6j6Wg");
}
}
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