JAR & JARM

Overview

JAR (JWT Secured Authorization Request, RFC 9101) and JARM (JWT Secured Authorization Response Mode) provide end-to-end integrity protection for the authorization flow:

• JAR — Authorization parameters are sent as a signed JWT (Request Object), preventing parameter tampering
• JARM — The authorization response is returned as a signed JWT, preventing response tampering

Together, they ensure that neither the authorization request nor the response can be modified by an attacker.

JAR (JWT Secured Authorization Request)

How JAR Works

Instead of passing authorization parameters as query string values, the client creates a signed JWT containing all parameters and sends it in the request parameter:

Standard:   /authorize?client_id=app&scope=openid&redirect_uri=...
With JAR:   /authorize?client_id=app&request=eyJhbGciOiJSUzI1NiJ9...

The JWT is signed with the client’s private key, ensuring the authorization server can verify that the parameters have not been modified.

JARBuilder

Create Request Objects using JARBuilder:

import { JARBuilder } from '@authrim/core';

const jarBuilder = new JARBuilder({
  signJwt: async (header, claims) => {
    // Sign the JWT with your private key
    return signedJwtString;
  },
  keyId: 'my-key-id',
  algorithm: 'RS256',
  lifetime: 300, // seconds
});

JARBuilderConfig

Parameter	Type	Default	Description
signJwt	(header, claims) => Promise<string>	Required	JWT signing function
keyId	string	—	Key ID (kid) for the JWT header
algorithm	string	'RS256'	Signing algorithm
lifetime	number	300	Request Object lifetime in seconds

Building a Request Object

const requestObject = await jarBuilder.buildRequestObject({
  clientId: 'my-app',
  issuer: 'https://auth.example.com',
  redirectUri: 'https://myapp.com/callback',
  scope: 'openid profile email',
  state: generatedState,
  nonce: generatedNonce,
  codeChallenge: generatedChallenge,
  codeChallengeMethod: 'S256',
});

// requestObject is a signed JWT string

JARRequestOptions

Parameter	Type	Description
clientId	string	OAuth 2.0 client ID
issuer	string	Authorization server issuer URL (used as aud)
redirectUri	string	Redirect URI
scope	string	Requested scopes
state	string	CSRF protection state
nonce	string	Replay protection nonce
codeChallenge	string	PKCE code challenge
codeChallengeMethod	string	Challenge method (always 'S256')
responseType	string	Response type (default: 'code')
prompt	string	Prompt behavior
loginHint	string	Login hint
acrValues	string	Authentication context
extraClaims	Record<string, unknown>	Additional JWT claims

Request Object JWT Claims

The generated JWT includes:

Claim	Description
iss	Client ID
aud	Authorization server issuer URL
iat	Issued at timestamp
exp	Expiration timestamp
jti	Unique identifier
nbf	Not before timestamp
response_type	OAuth response type
client_id	Client identifier
redirect_uri	Redirect URI
scope	Requested scopes
state	CSRF protection value
nonce	Replay protection value
code_challenge	PKCE code challenge
code_challenge_method	PKCE method

Using JAR with buildAuthorizationUrl

The simplest way to use JAR is through buildAuthorizationUrl():

const { url } = await client.buildAuthorizationUrl({
  redirectUri: 'https://myapp.com/callback',
  useJar: true,
});

Checking If JAR Is Required

import { isJarRequired } from '@authrim/core';

const discovery = await client.discover();

if (isJarRequired(discovery)) {
  // Server requires signed request objects
  const { url } = await client.buildAuthorizationUrl({
    redirectUri: 'https://myapp.com/callback',
    useJar: true,
  });
}

The isJarRequired() function checks the require_signed_request_object field in the discovery document.

---

JARM (JWT Secured Authorization Response Mode)

How JARM Works

Instead of returning authorization parameters as query string values, the authorization server returns a signed JWT in the response parameter:

Standard:   /callback?code=abc&state=xyz
With JARM:  /callback?response=eyJhbGciOiJSUzI1NiJ9...

The JWT is signed by the authorization server, ensuring the client can verify that the response has not been tampered with.

JARMValidator

Validate JARM responses using JARMValidator:

import { JARMValidator } from '@authrim/core';

const jarmValidator = new JARMValidator({
  verifyJwt: async (jwt, issuer) => {
    // Verify the JWT signature using the server's public key
    return decodedClaims;
  },
});

Validating a JARM Response

// Extract the response parameter from the callback URL
const responseJwt = JARMValidator.extractResponseFromCallback(callbackUrl);

if (responseJwt) {
  const result = await jarmValidator.validateResponse(discovery, responseJwt, {
    expectedState: storedState,
    clientId: 'my-app',
    clockSkewSeconds: 60,
  });

  console.log(result.code);   // Authorization code
  console.log(result.state);  // Validated state
}

JARMValidationOptions

Parameter	Type	Default	Description
expectedState	string	Required	Expected state value for CSRF validation
clientId	string	Required	Client ID (must match aud claim)
clockSkewSeconds	number	60	Allowed clock skew in seconds

JARMValidationResult

Property	Type	Description
code	string	The authorization code
state	string	The validated state parameter

JARM Response Claims

The JWT returned by the server contains:

Claim	Description
iss	Authorization server issuer
aud	Client ID
exp	Expiration timestamp
code	Authorization code (on success)
state	State parameter
error	Error code (on failure)
error_description	Error description (on failure)

Complete Example: JAR + JARM Flow

import { JARBuilder, JARMValidator, isJarRequired } from '@authrim/core';

// Setup
const jarBuilder = new JARBuilder({
  signJwt: mySignFunction,
  algorithm: 'RS256',
});

const jarmValidator = new JARMValidator({
  verifyJwt: myVerifyFunction,
});

// Step 1: Build authorization URL with JAR
const requestObject = await jarBuilder.buildRequestObject({
  clientId: 'my-app',
  issuer: 'https://auth.example.com',
  redirectUri: 'https://myapp.com/callback',
  scope: 'openid profile',
  state: generatedState,
  nonce: generatedNonce,
  codeChallenge: generatedChallenge,
  codeChallengeMethod: 'S256',
});

const authUrl = `${discovery.authorization_endpoint}?client_id=my-app&request=${requestObject}`;

// Step 2: After redirect, validate JARM response
const responseJwt = JARMValidator.extractResponseFromCallback(callbackUrl);

if (responseJwt) {
  const { code, state } = await jarmValidator.validateResponse(
    discovery,
    responseJwt,
    { expectedState: storedState, clientId: 'my-app' },
  );

  // Step 3: Exchange code for tokens
  const tokens = await exchangeCode(code);
}

Error Handling

Error Code	Description	Recovery
jar_signing_error	Failed to sign the Request Object	Check signing key and configuration
jar_required	Server requires JAR but it wasn’t used	Set useJar: true
jarm_validation_error	JARM response validation failed	Check server configuration
jarm_signature_invalid	JARM JWT signature verification failed	Verify server keys

References

• RFC 9101 — The OAuth 2.0 Authorization Framework: JWT-Secured Authorization Request (JAR)
• Financial-grade API Security Profile 2.0

Next Steps

• DPoP — Bind tokens to cryptographic keys
• PAR — Push authorization parameters via back-channel
• Authorization Code Flow — Standard login flow