authkestra_engine/token/
jwk.rs

1use crate::auth::error::AuthError;
2use jsonwebtoken::DecodingKey;
3use serde::{Deserialize, Serialize};
4
5/// A JSON Web Key, as published at `/jwks.json`.
6///
7/// This struct is widened (not an enum) so that every existing call site
8/// that builds a `Jwk` with a plain struct literal — inside this crate and
9/// downstream — keeps compiling: it only needs two more fields (`crv`, `x`),
10/// both `None` for the RSA shape it already builds. See the `to_decoding_key`
11/// doc comment for why an enum/`#[serde(untagged)]` representation was
12/// rejected in favor of this.
13///
14/// Two shapes are represented today:
15/// - RSA (`kty: "RSA"`): `n`, `e` are populated; `crv`, `x` are `None`.
16/// - OKP/Ed25519 (`kty: "OKP"`): `crv` (always `"Ed25519"`), `x` are
17///   populated; `n`, `e` are `None`.
18///
19/// `None` fields are omitted from the serialized JSON (`skip_serializing_if`)
20/// so each shape's wire format matches its RFC exactly: RFC 7517 §6.3.1 for
21/// RSA (`kty`, `n`, `e`), RFC 8037 §2 for OKP (`kty`, `crv`, `x`). Neither
22/// shape ever emits the other's fields, and neither emits a stray `"n":null`
23/// / `"x":null`.
24#[derive(Debug, Clone, Serialize, Deserialize)]
25pub struct Jwk {
26    #[serde(skip_serializing_if = "Option::is_none")]
27    pub kid: Option<String>,
28    pub kty: String,
29    #[serde(skip_serializing_if = "Option::is_none")]
30    pub alg: Option<String>,
31    /// RSA modulus (base64url, unpadded). `None` for OKP keys.
32    #[serde(skip_serializing_if = "Option::is_none")]
33    pub n: Option<String>,
34    /// RSA public exponent (base64url, unpadded). `None` for OKP keys.
35    #[serde(skip_serializing_if = "Option::is_none")]
36    pub e: Option<String>,
37    /// OKP subtype curve name, e.g. `"Ed25519"` (RFC 8037 §2). `None` for
38    /// RSA keys.
39    #[serde(skip_serializing_if = "Option::is_none")]
40    pub crv: Option<String>,
41    /// OKP public key (base64url, unpadded, RFC 8037 §2). `None` for RSA
42    /// keys.
43    #[serde(skip_serializing_if = "Option::is_none")]
44    pub x: Option<String>,
45}
46
47impl Jwk {
48    /// Derives a `DecodingKey` from this JWK, dispatching on `kty`.
49    ///
50    /// Supports `"RSA"` (unchanged from before this key gained the OKP
51    /// shape) and `"OKP"` with `crv: "Ed25519"` (RFC 8037). Any other `kty`,
52    /// or an OKP key advertising an unsupported curve, is rejected.
53    pub fn to_decoding_key(&self) -> Result<DecodingKey, AuthError> {
54        match self.kty.as_str() {
55            "RSA" => {
56                let n = self
57                    .n
58                    .as_ref()
59                    .ok_or_else(|| AuthError::Token("Missing 'n' component in JWK".to_string()))?;
60                let e = self
61                    .e
62                    .as_ref()
63                    .ok_or_else(|| AuthError::Token("Missing 'e' component in JWK".to_string()))?;
64
65                DecodingKey::from_rsa_components(n, e).map_err(|e| AuthError::Token(e.to_string()))
66            }
67            "OKP" => {
68                match self.crv.as_deref() {
69                    Some("Ed25519") => {}
70                    Some(other) => {
71                        return Err(AuthError::Token(format!(
72                            "Unsupported OKP curve '{}' in JWK",
73                            other
74                        )));
75                    }
76                    None => {
77                        return Err(AuthError::Token(
78                            "Missing 'crv' component in OKP JWK".to_string(),
79                        ));
80                    }
81                }
82
83                let x_str = self
84                    .x
85                    .as_ref()
86                    .ok_or_else(|| AuthError::Token("Missing 'x' component in JWK".to_string()))?;
87
88                authkestra_crypto_util::parse_ed25519_verifying_key_strict(x_str)
89                    .map_err(|e| AuthError::Token(e.to_string()))?;
90
91                DecodingKey::from_ed_components(x_str).map_err(|e| AuthError::Token(e.to_string()))
92            }
93            other => Err(AuthError::Token(format!(
94                "Unsupported JWK 'kty' '{}' — only RSA and OKP are supported",
95                other
96            ))),
97        }
98    }
99}
100
101#[cfg(test)]
102mod tests {
103    use super::*;
104
105    #[test]
106    fn rejects_low_order_ed25519_key() {
107        // The identity point: the canonical universal low-order vector.
108        let identity_b64 = "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
109        let jwk = Jwk {
110            kid: None,
111            kty: "OKP".to_string(),
112            alg: None,
113            n: None,
114            e: None,
115            crv: Some("Ed25519".to_string()),
116            x: Some(identity_b64.to_string()),
117        };
118
119        let err = jwk
120            .to_decoding_key()
121            .expect_err("should reject low order point");
122        assert!(
123            err.to_string().contains("low-order"),
124            "expected low-order point rejection, got: {}",
125            err
126        );
127    }
128}
authkestra_engine/token/jwk.rs

authkestra_engine/token/
jwk.rs
