systemprompt_security/jwt/
validate.rs

1//! The single RS256 decode primitive shared by every JWT validation path.
2//!
3//! Request-context middleware, session validation, hook-token validation, and
4//! the OAuth/MCP/agent domains all route through [`decode_rs256_claims`]. The
5//! `kid` lookup, RS256 enforcement, and the `exp`/`nbf`/issuer/audience policy
6//! live here and nowhere else, so the validators cannot drift apart. The only
7//! per-call knob is [`ValidationPolicy`].
8//!
9//! Audience validation is always on: every policy carries a non-empty expected
10//! audience set, and a policy that reaches the decoder with an empty set is
11//! rejected as [`AuthError::EmptyAudiencePolicy`] rather than silently
12//! accepting any `aud`. [`ValidationPolicy::session_context`] pins
13//! [`JwtAudience::FIRST_PARTY`], so a token minted for a narrower surface
14//! (`hook`, a custom resource) cannot ride the session middleware.
15//!
16//! Federated subject-token verification (token-exchange) is deliberately *not*
17//! a caller: it resolves keys from an external issuer's JWKS rather than this
18//! deployment's signing authority, so it is a genuinely different operation.
19
20use jsonwebtoken::{Algorithm, Validation, decode, decode_header};
21use systemprompt_models::auth::{JwtAudience, JwtClaims};
22
23use crate::error::{AuthError, AuthResult};
24use crate::keys::authority;
25
26pub const JWT_LEEWAY_SECONDS: u64 = 30;
27
28#[derive(Debug, Clone)]
29pub struct ValidationPolicy<'a> {
30    validate_exp: bool,
31    validate_nbf: bool,
32    leeway_seconds: u64,
33    issuer: Option<&'a str>,
34    audiences: &'a [JwtAudience],
35}
36
37impl<'a> ValidationPolicy<'a> {
38    #[must_use]
39    pub const fn session_context() -> Self {
40        Self {
41            validate_exp: true,
42            validate_nbf: true,
43            leeway_seconds: JWT_LEEWAY_SECONDS,
44            issuer: None,
45            audiences: JwtAudience::FIRST_PARTY,
46        }
47    }
48
49    #[must_use]
50    pub const fn issuer_scoped(issuer: &'a str, audiences: &'a [JwtAudience]) -> Self {
51        Self {
52            validate_exp: true,
53            validate_nbf: true,
54            leeway_seconds: JWT_LEEWAY_SECONDS,
55            issuer: Some(issuer),
56            audiences,
57        }
58    }
59}
60
61pub fn decode_rs256_claims(token: &str, policy: &ValidationPolicy<'_>) -> AuthResult<JwtClaims> {
62    if policy.audiences.is_empty() {
63        return Err(AuthError::EmptyAudiencePolicy);
64    }
65
66    let header = decode_header(token).map_err(AuthError::InvalidToken)?;
67    if header.alg != Algorithm::RS256 {
68        return Err(AuthError::UnsupportedAlgorithm {
69            got: format!("{:?}", header.alg),
70        });
71    }
72    let kid = header.kid.as_deref().ok_or(AuthError::MissingKid)?;
73    let key = authority::decoding_key_for_kid(kid)
74        .map_err(|e| AuthError::KeyLookup(e.to_string()))?
75        .ok_or_else(|| AuthError::UnknownKid(kid.to_owned()))?;
76
77    let mut validation = Validation::new(Algorithm::RS256);
78    validation.validate_exp = policy.validate_exp;
79    validation.validate_nbf = policy.validate_nbf;
80    validation.leeway = policy.leeway_seconds;
81    if let Some(issuer) = policy.issuer {
82        validation.set_issuer(&[issuer]);
83    }
84    let audience_strs: Vec<&str> = policy.audiences.iter().map(JwtAudience::as_str).collect();
85    validation.set_audience(&audience_strs);
86
87    decode::<JwtClaims>(token, key, &validation)
88        .map(|data| data.claims)
89        .map_err(AuthError::InvalidToken)
90}
systemprompt_security/jwt/validate.rs

systemprompt_security/jwt/
validate.rs
