oidc-token-hash

oidc-token-hash

oidc-token-hash validates (and generates) ID Token _hash claims such as at_hash or c_hash, shared component for oidc-provider and openid-client.

Its [*_hash] value is the base64url encoding of the left-most half of the hash of the octets of the ASCII representation of the token / state / code value, where the hash algorithm used is the hash algorithm used in the alg Header Parameter of the ID Token's JOSE Header. For instance, if the alg is RS256, hash the token / state / code value with SHA-256, then take the left-most 128 bits and base64url encode them. The *_hash value is a case sensitive string.

Matrix

JWS algorithm	used hash algorithm	Note
HS256, RS256, PS256, ES256, ES256K	sha256
HS384, RS384, PS384, ES384	sha384
HS512, RS512, PS512, ES512	sha512
EdDSA w/ Ed25519 curve	sha512	connect/issues#1125
EdDSA w/ Ed448 curve	shake256	connect/issues#1125

Usage

Validating

const oidcTokenHash = require('oidc-token-hash');

const access_token = 'YmJiZTAwYmYtMzgyOC00NzhkLTkyOTItNjJjNDM3MGYzOWIy9sFhvH8K_x8UIHj1osisS57f5DduL-ar_qw5jl3lthwpMjm283aVMQXDmoqqqydDSqJfbhptzw8rUVwkuQbolw';

oidcTokenHash.validate({ claim: 'at_hash', source: 'access_token' }, 'x7vk7f6BvQj0jQHYFIk4ag', access_token, 'RS256'); // => does not throw
oidcTokenHash.validate({ claim: 'at_hash', source: 'access_token' }, 'EGEAhGYyfuwDaVTifvrWSoD5MSy_5hZPy6I7Vm-7pTQ', access_token, 'EdDSA', 'Ed25519'); // => does not throw
oidcTokenHash.validate({ claim: 'at_hash', source: 'access_token' }, 'x7vk7f6BvQj0jQHYFIk4ag', 'foobar', 'RS256'); // => throws AssertionError, message: at_hash mismatch, expected w6uP8Tcg6K2QR905Rms8iQ, got: x7vk7f6BvQj0jQHYFIk4ag

Generating

// access_token from first example
oidcTokenHash.generate(access_token, 'RS256'); // => 'x7vk7f6BvQj0jQHYFIk4ag'
oidcTokenHash.generate(access_token, 'HS384'); // => 'ups_76_7CCye_J1WIyGHKVG7AAs2olYm'
oidcTokenHash.generate(access_token, 'ES512'); // => 'EGEAhGYyfuwDaVTifvrWSoD5MSy_5hZPy6I7Vm-7pTQ'
oidcTokenHash.generate(access_token, 'EdDSA', 'Ed25519'); // => 'EGEAhGYyfuwDaVTifvrWSoD5MSy_5hZPy6I7Vm-7pTQ'
oidcTokenHash.generate(access_token, 'EdDSA', 'Ed448'); // => 'jxsy68_eG9-91VnHsZ2VnA'

Changelog

• 4.0.0 - using sha512 for Ed25519 and shake256 for Ed448, refactored API, removed handling of none JWS alg
• 3.0.2 - removed base64url dependency
• 3.0.1 - base64url comeback
• 3.0.0 - drop lts/4 support, replace base64url dependency
• 2.0.0 - rather then assuming the alg based on the hash length #valid() now requires a third argument with the JOSE header alg value, resulting in strict validation
• 1.0.0 - initial release