.. _specs/rfc7523:

RFC7523: JWT Profile for OAuth 2.0 Client Authentication and Authorization Grants
=================================================================================

.. meta::
    :description: API references on RFC7523 JWT Bearer Grant of Python
        implementation, guide on how to create a server that support
        JWT profile for OAuth 2.0 client authentication and authorization
        grants.

This section contains the generic Python implementation of RFC7523_.

.. _RFC7523: https://tools.ietf.org/html/rfc7523

.. module:: authlib.oauth2.rfc7523


.. _jwt_grant_type:

Using JWTs as Authorization Grants
----------------------------------

JWT Profile for OAuth 2.0 Authorization Grants works in the same way with
:ref:`RFC6749 <specs/rfc6749>` built-in grants. Which means it can be
registered with :meth:`~authlib.oauth2.rfc6749.AuthorizationServer.register_grant`.

The base class is :class:`JWTBearerGrant`, you need to implement the missing
methods in order to use it. Here is an example::

    from authlib.jose import jwk
    from authlib.oauth2.rfc7523 import JWTBearerGrant as _JWTBearerGrant

    class JWTBearerGrant(_JWTBearerGrant):
        def authenticate_user(self, client, claims):
            # get user from claims info, usually it is claims['sub']
            # for anonymous user, return None
            return None

        def authenticate_client(self, claims):
            # get client from claims, usually it is claims['iss']
            # since the assertion JWT is generated by this client
            return get_client_by_iss(claims['iss'])

        def resolve_public_key(self, headers, payload):
            # get public key to decode the assertion JWT
            jwk_set = get_client_public_keys(claims['iss'])
            return jwk.loads(jwk_set, header.get('kid'))

    # register grant to authorization server
    authorization_server.register_grant(JWTBearerGrant)

When creating a client, authorization server will generate several key pairs.
The server itself can only keep the public keys, which will be used to decode
assertion value.

For **client implementation**, check out:

1. :class:`~authlib.integrations.requests_client.AssertionSession`.
2. :class:`~authlib.integrations.httpx_client.AssertionSession`.
3. :class:`~authlib.integrations.httpx_client.AsyncAssertionSession`.

.. _jwt_client_authentication:

Using JWTs for Client Authentication
------------------------------------

In :ref:`specs/rfc6749`, Authlib provided three built-in client authentication
methods, which are ``none``, ``client_secret_post`` and ``client_secret_basic``.
With the power of Assertion Framework, we can add more client authentication
methods. In this section, Authlib provides two more options:
``client_secret_jwt`` and ``private_key_jwt``. RFC7523 itself doesn't define
any names, these two names are defined by OpenID Connect in ClientAuthentication_.

The :class:`~authlib.oauth2.rfc6749.AuthorizationServer` has provided a method
:meth:`~authlib.oauth2.rfc6749.AuthorizationServer.register_client_auth_method`
to add more client authentication methods.

In Authlib, ``client_secret_jwt`` and ``private_key_jwt`` share the same API,
using :class:`JWTBearerClientAssertion` to create a new client authentication::

    class JWTClientAuth(JWTBearerClientAssertion):
        def validate_jti(self, claims, jti):
            # validate_jti is required by OpenID Connect
            # but it is optional by RFC7523
            # use cache to validate jti value
            key = 'jti:{}-{}'.format(claims['sub'], jti)
            if cache.get(key):
                return False
            cache.set(key, 1, timeout=3600)
            return True

        def resolve_client_public_key(self, client, headers):
            if headers['alg'] == 'HS256':
                return client.client_secret
            if headers['alg'] == 'RS256':
                return client.public_key
            # you may support other ``alg`` value

    authorization_server.register_client_auth_method(
        JWTClientAuth.CLIENT_AUTH_METHOD,
        JWTClientAuth('https://example.com/oauth/token')
    )

The value ``https://example.com/oauth/token`` is your authorization servers's
token endpoint, which is used as ``aud`` value in JWT.

Now we have added this client auth method to authorization server, but no
grant types support this authentication method, you need to add it to the
supported grant types too, e.g. we want to support this in authorization
code grant::

    from authlib.oauth2.rfc6749 import grants

    class AuthorizationCodeGrant(grants.AuthorizationCodeGrant):
        TOKEN_ENDPOINT_AUTH_METHODS = [
            'client_secret_basic',
            JWTClientAuth.CLIENT_AUTH_METHOD,
        ]
        # ...

You may noticed that the value of ``CLIENT_AUTH_METHOD`` is
``client_assertion_jwt``. It is not ``client_secret_jwt`` or
``private_key_jwt``, because they have the same logic. In the above
implementation::

    def resolve_client_public_key(self, client, headers):
        alg = headers['alg']

If this ``alg`` is a MAC SHA like ``HS256``, it is called ``client_secret_jwt``,
because the key used to sign a JWT is the client's ``client_secret`` value. If
this ``alg`` is ``RS256`` or something else, it is called ``private_key_jwt``,
because client will use its private key to sign the JWT. You can set a limitation
in the implementation of ``resolve_client_public_key`` to accept only ``HS256``
alg, in this case, you can also alter ``CLIENT_AUTH_METHOD = 'client_secret_jwt'``.

.. _ClientAuthentication: http://openid.net/specs/openid-connect-core-1_0.html#ClientAuthentication

.. _jwt_oauth2session:

Using JWTs Client Assertion in OAuth2Session
--------------------------------------------

Authlib RFC7523 provides two more client authentication methods for :ref:`oauth_2_session`:

1. ``client_secret_jwt``
2. ``private_key_jwt``

Here is an example of how to register ``client_secret_jwt`` for ``OAuth2Session``::

    from authlib.oauth2.rfc7523 import ClientSecretJWT
    from authlib.integrations.requests_client import OAuth2Session

    session = OAuth2Session(
        'your-client-id', 'your-client-secret',
        token_endpoint_auth_method='client_secret_jwt'
    )
    token_endpoint = 'https://example.com/oauth/token'
    session.register_client_auth_method(ClientSecretJWT(token_endpoint))
    session.fetch_token(token_endpoint)

How about ``private_key_jwt``? It is the same as ``client_secret_jwt``::

    from authlib.oauth2.rfc7523 import PrivateKeyJWT

    with open('your-private-key.pem', 'rb') as f:
        private_key = f.read()

    session = OAuth2Session(
        'your-client-id', private_key,
        token_endpoint_auth_method='private_key_jwt'  # NOTICE HERE
    )
    token_endpoint = 'https://example.com/oauth/token'
    session.register_client_auth_method(PrivateKeyJWT(token_endpoint))
    session.fetch_token(token_endpoint)

API Reference
-------------

.. autoclass:: JWTBearerGrant
    :member-order: bysource
    :members:

.. autoclass:: JWTBearerClientAssertion
    :member-order: bysource
    :members:

.. autoclass:: ClientSecretJWT

.. autoclass:: PrivateKeyJWT
