# Register Grants

There are four grant types defined by RFC6749, you can also create your own extended grant. Register the supported grant types to the authorization server.

## Authorization Code Grant

Authorization Code Grant is a very common grant type, it is supported by almost every OAuth 2 providers. It uses an authorization code to exchange access tokens. In this case, we need a place to store the authorization code. It can be kept in a database or a cache like redis. Here is a SQLAlchemy mixin for AuthorizationCode:

    from authlib.integrations.sqla_oauth2 import OAuth2AuthorizationCodeMixin

    class AuthorizationCode(db.Model, OAuth2AuthorizationCodeMixin):
        id = db.Column(db.Integer, primary_key=True)
        user_id = db.Column(
            db.Integer, db.ForeignKey('user.id', ondelete='CASCADE')
        )
        user = db.relationship('User')

Implement this grant by subclassing `AuthorizationCodeGrant`:

    from authlib.oauth2.rfc6749 import grants

    class AuthorizationCodeGrant(grants.AuthorizationCodeGrant):
        def save_authorization_code(self, code, request):
            client = request.client
            auth_code = AuthorizationCode(
                code=code,
                client_id=client.client_id,
                redirect_uri=request.redirect_uri,
                scope=request.scope,
                user_id=request.user.id,
            )
            db.session.add(auth_code)
            db.session.commit()
            return auth_code

        def query_authorization_code(self, code, client):
            item = AuthorizationCode.query.filter_by(
                code=code, client_id=client.client_id).first()
            if item and not item.is_expired():
                return item

        def delete_authorization_code(self, authorization_code):
            db.session.delete(authorization_code)
            db.session.commit()

        def authenticate_user(self, authorization_code):
            return User.query.get(authorization_code.user_id)

    # register it to grant endpoint
    server.register_grant(AuthorizationCodeGrant)

Note

AuthorizationCodeGrant is the most complex grant.

Default allowed Client Authentication Methods are:

1. client_secret_basic

2. client_secret_post

3. none

You can change it in the subclass, e.g. remove the `none` authentication method:

    class AuthorizationCodeGrant(grants.AuthorizationCodeGrant):
        TOKEN_ENDPOINT_AUTH_METHODS = ['client_secret_basic', 'client_secret_post']

Note

This is important when you want to support OpenID Connect.

## Implicit Grant

The implicit grant type is usually used in a browser, when resource owner granted the access, an access token is issued in the redirect URI, there is no missing implementation, which means it can be easily registered with:

    from authlib.oauth2.rfc6749 import grants

    # register it to grant endpoint
    server.register_grant(grants.ImplicitGrant)

Implicit Grant is used by public clients which have no client_secret. Default allowed Client Authentication Methods: `none`.

## Resource Owner Password Credentials Grant

The resource owner uses its username and password to exchange an access token. This grant type should be used only when the client is trustworthy; implement it with a subclass of `ResourceOwnerPasswordCredentialsGrant`:

    from authlib.oauth2.rfc6749 import grants

    class PasswordGrant(grants.ResourceOwnerPasswordCredentialsGrant):
        def authenticate_user(self, username, password):
            user = User.query.filter_by(username=username).first()
            if user.check_password(password):
                return user

    # register it to grant endpoint
    server.register_grant(PasswordGrant)

Default allowed Client Authentication Methods: `client_secret_basic`. You can add more in the subclass:

    class PasswordGrant(grants.ResourceOwnerPasswordCredentialsGrant):
        TOKEN_ENDPOINT_AUTH_METHODS = [
            'client_secret_basic', 'client_secret_post'
        ]

## Client Credentials Grant

Client credentials grant type can access public resources and MAYBE the client’s creator’s resources, depending on how you issue tokens to this grant type. It can be easily registered with:

    from authlib.oauth2.rfc6749 import grants

    # register it to grant endpoint
    server.register_grant(grants.ClientCredentialsGrant)

Default allowed Client Authentication Methods: `client_secret_basic`. You can add more in the subclass:

    class ClientCredentialsGrant(grants.ClientCredentialsGrant):
        TOKEN_ENDPOINT_AUTH_METHODS = [
            'client_secret_basic', 'client_secret_post'
        ]

## Refresh Token Grant

Many OAuth 2 providers do not implement a refresh token endpoint. Authlib provides it as a grant type; implement it with a subclass of `RefreshTokenGrant`:

    from authlib.oauth2.rfc6749 import grants

    class RefreshTokenGrant(grants.RefreshTokenGrant):
        def authenticate_refresh_token(self, refresh_token):
            item = Token.query.filter_by(refresh_token=refresh_token).first()
            # define is_refresh_token_valid by yourself
            # usually, you should check if refresh token is expired and revoked
            if item and item.is_refresh_token_valid():
                return item

        def authenticate_user(self, credential):
            return User.query.get(credential.user_id)

        def revoke_old_credential(self, credential):
            credential.revoked = True
            db.session.add(credential)
            db.session.commit()

    # register it to grant endpoint
    server.register_grant(RefreshTokenGrant)

Default allowed Client Authentication Methods: `client_secret_basic`. You can add more in the subclass:

    class RefreshTokenGrant(grants.RefreshTokenGrant):
        TOKEN_ENDPOINT_AUTH_METHODS = [
            'client_secret_basic', 'client_secret_post'
        ]

By default, RefreshTokenGrant will not issue a `refresh_token` in the token response. Developers can change this behavior with:

    class RefreshTokenGrant(grants.RefreshTokenGrant):
        INCLUDE_NEW_REFRESH_TOKEN = True

## Custom Grant Types

It is also possible to create your own grant types. In Authlib, a Grant supports two endpoints:

1. Authorization Endpoint: which can handle requests with `response_type`.

2. Token Endpoint: which is the endpoint to issue tokens.

Changed in version v0.12: Using `AuthorizationEndpointMixin` and `TokenEndpointMixin` instead of `AUTHORIZATION_ENDPOINT=True` and `TOKEN_ENDPOINT=True`.

Creating a custom grant type with BaseGrant:

    from authlib.oauth2.rfc6749.grants import (
        BaseGrant, AuthorizationEndpointMixin, TokenEndpointMixin
    )

    class MyCustomGrant(BaseGrant, AuthorizationEndpointMixin, TokenEndpointMixin):
        GRANT_TYPE = 'custom-grant-type-name'

        def validate_authorization_request(self):
            # only needed if using AuthorizationEndpointMixin

        def create_authorization_response(self, grant_user):
            # only needed if using AuthorizationEndpointMixin

        def validate_token_request(self):
            # only needed if using TokenEndpointMixin

        def create_token_response(self):
            # only needed if using TokenEndpointMixin

For a better understanding, you can read the source code of the built-in grant types. And there are extended grant types defined by other specs:

1. Using JWTs as Authorization Grants

## Grant Extensions

New in version 0.10.

Grants can accept extensions. Developers can pass extensions when registering grants:

    authorization_server.register_grant(AuthorizationCodeGrant, [extension])

For instance, there is the `CodeChallenge` extension in Authlib:

    server.register_grant(AuthorizationCodeGrant, [CodeChallenge(required=False)])

Learn more about `CodeChallenge` at RFC7636: Proof Key for Code Exchange by OAuth Public Clients.