cedarling 0.0.49

// This software is available under the Apache-2.0 license.
// See https://www.apache.org/licenses/LICENSE-2.0.txt for full text.
//
// Copyright (c) 2024, Gluu, Inc.

use base64::{Engine, prelude::BASE64_URL_SAFE_NO_PAD};
use jsonwebtoken::Algorithm;
use serde::Deserialize;
use serde_json::Value;

/// A decoded but not validated JWT.
///
/// We need to decode the header and the `iss` claim in order to fetch the right
/// validation key.
#[derive(Debug, PartialEq)]
pub(crate) struct DecodedJwt {
    pub header: DecodedJwtHeader,
    pub claims: DecodedJwtClaims,
}

/// See [`RFC 7515 Section 4.1`] for the registered header parameter names.
///
/// [`RFC 7515 Section 4.1`]: https://datatracker.ietf.org/doc/html/rfc7515#section-4.1
#[derive(Debug, Deserialize, PartialEq)]
pub(crate) struct DecodedJwtHeader {
    pub typ: Option<String>,
    pub cty: Option<String>,
    pub kid: Option<String>,
    pub alg: Algorithm,
}

/// See [`RFC 7419 Section 4.1`] for the registered claim names.
///
/// [`RFC 7515 Section 4.1`]: https://datatracker.ietf.org/doc/html/rfc7519#section-4.1
#[derive(Debug, Deserialize, PartialEq)]
pub(crate) struct DecodedJwtClaims {
    #[serde(flatten)]
    pub inner: Value,
}

pub(crate) fn decode_jwt(jwt: &str) -> Result<DecodedJwt, DecodeJwtError> {
    let split = jwt.split('.').collect::<Vec<&str>>();
    if split.len() != 3 {
        return Err(DecodeJwtError::InvalidJwtFormat);
    }

    let decoded_header = BASE64_URL_SAFE_NO_PAD
        .decode(split[0])
        .map_err(DecodeJwtError::DecodeHeader)?;
    let header = serde_json::from_slice::<DecodedJwtHeader>(&decoded_header)
        .map_err(DecodeJwtError::DeserializeHeader)?;

    let decoded_claims = BASE64_URL_SAFE_NO_PAD
        .decode(split[1])
        .map_err(DecodeJwtError::DecodeClaims)?;
    let claims = serde_json::from_slice::<DecodedJwtClaims>(&decoded_claims)
        .map_err(DecodeJwtError::DeserializeClaims)?;

    Ok(DecodedJwt { header, claims })
}

#[derive(Debug, thiserror::Error)]
pub enum DecodeJwtError {
    #[error("the JWT is not in the form 'header.payload.signature'")]
    InvalidJwtFormat,
    #[error("error while decoding the JWT's header: {0}")]
    DecodeHeader(#[source] base64::DecodeError),
    #[error("error while deserializing the JWT's header: {0}")]
    DeserializeHeader(#[source] serde_json::Error),
    #[error("error while decoding the JWT's claims: {0}")]
    DecodeClaims(#[source] base64::DecodeError),
    #[error("error while deserializing the JWT's claims: {0}")]
    DeserializeClaims(#[source] serde_json::Error),
}

#[cfg(test)]
mod test {
    use super::*;
    use serde_json::json;
    use test_utils::assert_eq;

    #[test]
    fn can_decode_jwt() {
        let jwt = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c";

        let jwt = decode_jwt(jwt).expect("decode jwt successfully");

        assert_eq!(
            jwt,
            DecodedJwt {
                header: DecodedJwtHeader {
                    typ: Some("JWT".into()),
                    alg: Algorithm::HS256,
                    cty: None,
                    kid: None,
                },
                claims: DecodedJwtClaims {
                    inner: json!({
                        "sub": "1234567890",
                        "name": "John Doe",
                        "iat": 1_516_239_022,
                    })
                }
            }
        );
    }

    #[test]
    fn errors_on_invalid_jwt_format() {
        let cases = [
            "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c",
            "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c",
            "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ",
        ];

        for (i, jwt) in cases.into_iter().enumerate() {
            let err = decode_jwt(jwt).expect_err("should error while decoding jwt");

            assert!(
                matches!(err, DecodeJwtError::InvalidJwtFormat),
                "failed assertion in case: {i}"
            );
        }
    }
}