Crate jwt_compact

Minimalistic JSON web token (JWT) implementation with focus on type safety and secure cryptographic primitives.

Design choices

• JWT signature algorithms (i.e., cryptographic algorithms providing JWT integrity) are expressed via the Algorithm trait, which uses fully typed keys and signatures.
• JWT header is represented by the Header struct. Notably, Header does not expose the alg field. Instead, alg is filled automatically during token creation, and is compared to the expected value during verification. (If you do not know the JWT signature algorithm during verification, you’re doing something wrong.) This eliminates the possibility of algorithm switching attacks.

Additional features

• The crate supports more compact CBOR encoding of the claims. This feature is enabled via the ciborium feature.
• The crate supports EdDSA algorithm with the Ed25519 elliptic curve, and ES256K algorithm with the secp256k1 elliptic curve.
• Supports basic JSON Web Key functionality, e.g., for converting keys to / from JSON or computing a key thumbprint.

Supported algorithms

Algorithm(s)	Feature	Description
HS256, HS384, HS512	-	Uses pure Rust sha2 crate
EdDSA (Ed25519)	exonum-crypto	libsodium binding
EdDSA (Ed25519)	ed25519-dalek	Pure Rust implementation
EdDSA (Ed25519)	ed25519-compact	Compact pure Rust implementation, WASM-compatible
ES256K	es256k	Rust binding for libsecp256k1
ES256K	k256	Pure Rust implementation
ES256	p256	Pure Rust implementation
RS*, PS* (RSA)	rsa	Uses pure Rust rsa crate with blinding

EdDSA and ES256K algorithms are somewhat less frequently supported by JWT implementations than others since they are recent additions to the JSON Web Algorithms (JWA) suit. They both work with elliptic curves (Curve25519 and secp256k1; both are widely used in crypto community and believed to be securely generated). These algs have 128-bit security, making them an alternative to ES256.

RSA support requires a system-wide RNG retrieved via the getrandom crate. In case of a compilation failure in the getrandom crate, you may want to include it as a direct dependency and specify one of its features to assist getrandom with choosing an appropriate RNG implementation; consult getrandom docs for more details. See also WASM and bare-metal E2E tests included in the source code repository of this crate.

CBOR support

If the ciborium crate feature is enabled (and it is enabled by default), token claims can be encoded using CBOR with the AlgorithmExt::compact_token() method. The compactly encoded JWTs have the cty field (content type) in their header set to "CBOR". Tokens with such encoding can be verified in the same way as ordinary tokens; see examples below.

If the ciborium feature is disabled, AlgorithmExt::compact_token() is not available. Verifying CBOR-encoded tokens in this case is not supported either; a ParseError::UnsupportedContentType will be returned when creating an UntrustedToken from the token string.

no_std support

The crate supports a no_std compilation mode. This is controlled by two features: clock and std; both are on by default.

• The clock feature enables getting the current time using Utc::now() from chrono. Without it, some TimeOptions constructors, such as the Default impl, are not available. It is still possible to create TimeOptions with an explicitly specified clock function, or to set / verify time-related Claims fields manually.
• The std feature is propagated to the core dependencies and enables std-specific functionality (such as error types implementing the standard Error trait).

Some alloc types are still used in the no_std mode, such as String, Vec and Cow.

Note that not all crypto backends are no_std-compatible.

Examples

Basic JWT lifecycle:

use chrono::{Duration, Utc};
use jwt_compact::{prelude::*, alg::{Hs256, Hs256Key}};
use serde::{Serialize, Deserialize};

/// Custom claims encoded in the token.
#[derive(Debug, PartialEq, Serialize, Deserialize)]
struct CustomClaims {
    /// `sub` is a standard claim which denotes claim subject:
    /// https://tools.ietf.org/html/rfc7519#section-4.1.2
    #[serde(rename = "sub")]
    subject: String,
}

// Choose time-related options for token creation / validation.
let time_options = TimeOptions::default();
// Create a symmetric HMAC key, which will be used both to create and verify tokens.
let key = Hs256Key::new(b"super_secret_key_donut_steel");
// Create a token.
let header = Header::empty().with_key_id("my-key");
let claims = Claims::new(CustomClaims { subject: "alice".to_owned() })
    .set_duration_and_issuance(&time_options, Duration::days(7))
    .set_not_before(Utc::now() - Duration::hours(1));
let token_string = Hs256.token(&header, &claims, &key)?;
println!("token: {token_string}");

// Parse the token.
let token = UntrustedToken::new(&token_string)?;
// Before verifying the token, we might find the key which has signed the token
// using the `Header.key_id` field.
assert_eq!(token.header().key_id, Some("my-key".to_owned()));
// Validate the token integrity.
let token: Token<CustomClaims> = Hs256.validator(&key).validate(&token)?;
// Validate additional conditions.
token.claims()
    .validate_expiration(&time_options)?
    .validate_maturity(&time_options)?;
// Now, we can extract information from the token (e.g., its subject).
let subject = &token.claims().custom.subject;
assert_eq!(subject, "alice");

Compact JWT

/// Custom claims encoded in the token.
#[derive(Debug, PartialEq, Serialize, Deserialize)]
struct CustomClaims {
    /// `sub` is a standard claim which denotes claim subject:
    ///     https://tools.ietf.org/html/rfc7519#section-4.1.2
    /// The custom serializer we use allows to efficiently
    /// encode the subject in CBOR.
    #[serde(rename = "sub", with = "HexForm")]
    subject: [u8; 32],
}

let time_options = TimeOptions::default();
let key = Hs256Key::new(b"super_secret_key_donut_steel");
let claims = Claims::new(CustomClaims { subject: [111; 32] })
    .set_duration_and_issuance(&time_options, Duration::days(7));
let token = Hs256.token(&Header::empty(), &claims, &key)?;
println!("token: {token}");
let compact_token = Hs256.compact_token(&Header::empty(), &claims, &key)?;
println!("compact token: {compact_token}");
// The compact token should be ~40 chars shorter.

// Parse the compact token.
let token = UntrustedToken::new(&compact_token)?;
let token: Token<CustomClaims> = Hs256.validator(&key).validate(&token)?;
token.claims().validate_expiration(&time_options)?;
// Now, we can extract information from the token (e.g., its subject).
assert_eq!(token.claims().custom.subject, [111; 32]);

JWT with custom header fields

#[derive(Debug, PartialEq, Serialize, Deserialize)]
struct CustomClaims { subject: [u8; 32] }

/// Additional fields in the token header.
#[derive(Debug, Clone, Serialize, Deserialize)]
struct HeaderExtensions { custom: bool }

let time_options = TimeOptions::default();
let key = Hs256Key::new(b"super_secret_key_donut_steel");
let claims = Claims::new(CustomClaims { subject: [111; 32] })
    .set_duration_and_issuance(&time_options, Duration::days(7));
let header = Header::new(HeaderExtensions { custom: true })
    .with_key_id("my-key");
let token = Hs256.token(&header, &claims, &key)?;
print!("token: {token}");

// Parse the token.
let token: UntrustedToken<HeaderExtensions> =
    token.as_str().try_into()?;
// Token header (incl. custom fields) can be accessed right away.
assert_eq!(token.header().key_id.as_deref(), Some("my-key"));
assert!(token.header().other_fields.custom);
// Token can then be validated as usual.
let token = Hs256.validator::<CustomClaims>(&key).validate(&token)?;
assert_eq!(token.claims().custom.subject, [111; 32]);

Modules

• alg
  Implementations of JWT signing / verification algorithms. Also contains generic traits for signing and verifying keys.
• jwk
  Basic support of JSON Web Keys (JWK).
• prelude
  Prelude to neatly import all necessary stuff from the crate.

Structs

• Claims
  Claims encoded in a token.
• Empty
  A structure with no fields that can be used as a type parameter to Claims.
• Header
  JWT header.
• Renamed
  Algorithm that uses a custom name when creating and validating tokens.
• SignedToken
  Token together with the validated token signature.
• TimeOptions
  Time-related options for token creation and validation.
• Token
  Token with validated integrity.
• UntrustedToken
  Parsed, but unvalidated token.
• Validator
  Validator for a certain signing Algorithm associated with a specific verifying key and a claims type. Produced by the AlgorithmExt::validator() method.

Enums

• Claim
  Identifier of a claim in Claims.
• CreationError
  Errors that can occur during token creation.
• ParseError
  Errors that may occur during token parsing.
• Thumbprint
  Representation of a X.509 certificate thumbprint (x5t and x5t#S256 fields in the JWT Header).
• ValidationError
  Errors that can occur during token validation.

Traits

• Algorithm
  JWT signing algorithm.
• AlgorithmExt
  Automatically implemented extensions of the Algorithm trait.
• AlgorithmSignature
  Signature for a certain JWT signing Algorithm.