jwk-simple

[!WARNING] This project is a work in progress. The API may change.

A Rust library for working with JSON Web Keys (JWK) and JWK Sets (JWKS) as defined in RFC 7517, with WASM compatibility and optional jwt-simple integration.

Features

• Full RFC compliance: Supports RFC 7517 (JWK), RFC 7518 (algorithms), RFC 8037 (EdDSA), and RFC 7638 (thumbprints)
• Multiple key types: RSA, EC (P-256, P-384, P-521, secp256k1), Symmetric (HMAC), and OKP (Ed25519, Ed448, X25519, X448)
• WASM compatible: Core functionality works in WebAssembly environments
• Security-first: Zeroize support for sensitive data, constant-time comparisons
• jwt-simple integration: Optional feature for converting JWKs to jwt-simple key types
• Remote fetching: Load JWKS from HTTP endpoints with caching support
• Caching: Optional TTL-based caching of decoded keys

Quick Start

Add to your Cargo.toml:

[dependencies]
jwk-simple = "0.1"

Parse a JWKS and find a key:

use jwk_simple::KeySet;

let json = r#"{
    "keys": [{
        "kty": "RSA",
        "kid": "my-key-id",
        "use": "sig",
        "n": "0vx7agoebGcQSuuPiLJXZptN9nndrQmbXEps2aiAFbWhM78LhWx4cbbfAAtVT86zwu1RK7aPFFxuhDR1L6tSoc_BJECPebWKRXjBZCiFV4n3oknjhMstn64tZ_2W-5JsGY4Hc5n9yBXArwl93lqt7_RN5w6Cf0h4QyQ5v-65YGjQR0_FDW2QvzqY368QQMicAtaSqzs8KJZgnYb9c7d0zgdAZHzu6qMQvRL5hajrn1n91CbOpbISD08qNLyrdkt-bFTWhAI4vMQFh6WeZu0fM4lFd2NcRwr3XPksINHaQ-G_xBniIqbw0Ls1jF44-csFCur-kEgU8awapJzKnqDKgw",
        "e": "AQAB"
    }]
}"#;

let jwks: KeySet = serde_json::from_str(json)?;
let key = jwks.find_by_kid("my-key-id").expect("key not found");
assert!(key.is_public_key_only());

Feature Flags

Usage Examples

Basic JWKS Parsing

use jwk_simple::{KeySet, KeyType, KeyUse};

// Parse from JSON string
let jwks: KeySet = serde_json::from_str(json)?;

// Find keys by various criteria
let key = jwks.find_by_kid("key-id");
let rsa_keys = jwks.find_by_kty(KeyType::Rsa);
let signing_keys = jwks.find_by_use(KeyUse::Signature);

// Get the first signing key (common pattern)
let first_signing = jwks.first_signing_key();

// Iterate over all keys
for key in &jwks {
    println!("Key: {:?}", key.kid);
}

Converting to jwt-simple Keys

With the jwt-simple feature enabled:

use jwk_simple::KeySet;
use jwt_simple::prelude::*;

let jwks: KeySet = serde_json::from_str(json)?;
let jwk = jwks.find_by_kid("my-key").unwrap();

// Convert to jwt-simple key type using TryFrom/TryInto
let key: RS256PublicKey = jwk.try_into()?;

// Verify a JWT
let claims = key.verify_token::<NoCustomClaims>(&token, None)?;

Fetching from HTTP

With the http feature enabled:

use jwk_simple::{KeySource, RemoteKeySet, InMemoryCachedKeySet};
use std::time::Duration;

// Create remote key set (uses default 30s timeout)
let remote = RemoteKeySet::new("https://example.com/.well-known/jwks.json");

// For custom timeout, use a custom client
let client = reqwest::Client::builder()
    .timeout(Duration::from_secs(10))
    .build()?;
let remote = RemoteKeySet::new_with_client(
    "https://example.com/.well-known/jwks.json",
    client,
);

// Fetch the JWKS
let jwks = remote.get_keyset().await?;

// For production, wrap with caching (5 minute TTL)
let cached = InMemoryCachedKeySet::with_ttl(
    RemoteKeySet::new("https://example.com/.well-known/jwks.json"),
    Duration::from_secs(300),
);
let key = cached.get_key("my-key-id").await?;

Caching Keys

With the http feature enabled:

use jwk_simple::{InMemoryKeyCache, InMemoryCachedKeySet, KeyCache, KeySource, RemoteKeySet};
use std::time::Duration;

// Create a cached remote key source
let cached = InMemoryCachedKeySet::with_ttl(
    RemoteKeySet::new("https://example.com/.well-known/jwks.json"),
    Duration::from_secs(300), // 5 minute TTL
);

// Keys are automatically cached on first access
let key = cached.get_key("key-id").await?;

// Invalidate the entire cache when needed
cached.invalidate().await;

// Or invalidate a specific key
cached.invalidate_key("key-id").await;

JWK Thumbprints (RFC 7638)

use jwk_simple::KeySet;

let jwks: KeySet = serde_json::from_str(json)?;
let key = jwks.first().unwrap();

// Calculate thumbprint (base64url-encoded SHA-256)
let thumbprint = key.thumbprint();

// Find key by thumbprint
let key = jwks.find_by_thumbprint(&thumbprint);

Supported Key Types

RSA (kty: "RSA")

• Public keys: n, e
• Private keys: n, e, d, p, q, dp, dq, qi
• Algorithms: RS256, RS384, RS512, PS256, PS384, PS512

Elliptic Curve (kty: "EC")

• Curves: P-256, P-384, P-521, secp256k1
• Public keys: crv, x, y
• Private keys: crv, x, y, d
• Algorithms: ES256, ES384, ES512, ES256K

Symmetric (kty: "oct")

• Keys: k
• Algorithms: HS256, HS384, HS512, A128KW, A192KW, A256KW

Octet Key Pair (kty: "OKP")

• Curves: Ed25519, Ed448, X25519, X448
• Public keys: crv, x
• Private keys: crv, x, d
• Algorithms: EdDSA

Comparison to Other Libraries

When to use jwk-simple

• You need jwt-simple integration - Direct conversion to jwt-simple key types
• You're building Cloudflare Workers - Native KV cache support
• You need WASM support - Core parsing works in browser
• You want full spec compliance - All key types including OKP

When to use alternatives

• jwks-client - If you only need RSA and want mature async HTTP
• jsonwebkey - If you need key generation and PEM/DER conversion
• jwt-simple - If you only need JWT operations, not JWKS
• jsonwebtoken - If you want the most widely-used JWT library

Security Considerations

This crate prioritizes security:

• Zeroize: Private key parameters are zeroed from memory on drop via the zeroize crate
• Constant-time base64: Base64 encoding uses constant-time operations via base64ct
• Debug redaction: Debug output redacts sensitive key material
• No panics: All public functions return Result types
• Input validation: Key parameters are validated for correct sizes

WASM Usage

Core JWKS parsing works in WebAssembly environments. The following features are NOT available in WASM:

• http - No async HTTP in WASM (use browser fetch and pass JSON string)
• File-based sources - No filesystem access

Example for WASM:

use jwk_simple::KeySet;

// In WASM, fetch JWKS via browser APIs, then parse
let jwks: KeySet = serde_json::from_str(&json_string)?;
let key = jwks.find_by_kid("key-id").expect("key not found");

License

The project is licensed under the MIT License.