# Flask OIDC Provider

OpenID Connect 1.0 is supported since version 0.6. The integrations are built with Custom Grant Types and Grant Extensions. Since OpenID Connect is built on OAuth 2.0 frameworks, you need to read Flask OAuth 2.0 Server at first.

Changed in version v0.12: The Grant system has been redesigned from v0.12. This documentation ONLY works for Authlib >=v0.12.

Looking for OpenID Connect Client? Head over to Flask OAuth Client.

## Understand JWT

OpenID Connect 1.0 uses JWT a lot. Make sure you have the basic understanding of JOSE Guide.

For OpenID Connect, we need to understand at least four concepts:

1. alg: Algorithm for JWT

2. key: Private key for JWT

3. iss: Issuer value for JWT

4. exp: JWT expires time

### alg

The algorithm to sign a JWT. This is the `alg` value defined in header part of a JWS:

    {"alg": "RS256"}

The available algorithms are defined in RFC7518: JSON Web Algorithms, which are:

- HS256: HMAC using SHA-256

- HS384: HMAC using SHA-384

- HS512: HMAC using SHA-512

- RS256: RSASSA-PKCS1-v1_5 using SHA-256

- RS384: RSASSA-PKCS1-v1_5 using SHA-384

- RS512: RSASSA-PKCS1-v1_5 using SHA-512

- ES256: ECDSA using P-256 and SHA-256

- ES384: ECDSA using P-384 and SHA-384

- ES512: ECDSA using P-521 and SHA-512

- PS256: RSASSA-PSS using SHA-256 and MGF1 with SHA-256

- PS384: RSASSA-PSS using SHA-384 and MGF1 with SHA-384

- PS512: RSASSA-PSS using SHA-512 and MGF1 with SHA-512

The HMAC using SHA algorithms are not suggested since you need to share secrets between server and client. Most OpenID Connect services are using `RS256`.

### key

A private key is required to generate a JWT. The key that you are going to use dependents on the `alg` you are using. For instance, the alg is `RS256`, you need to use an RSA private key. It can be set with:

    key = '''-----BEGIN RSA PRIVATE KEY-----\nMIIEog...'''

    # or in JWK format
    key = {"kty": "RSA", "n": ...}

### iss

The `iss` value in the JWT payload. The value can be your website name or URL. For example, Google is using:

    {"iss": "https://accounts.google.com"}

## Code Flow

OpenID Connect authorization code flow relies on the OAuth2 authorization code flow and extends it.

OpenID Connect Code flow is the same as Authorization Code flow, but with extended features. We can apply the `OpenIDCode` extension to Authorization Code Grant.

First, we need to implement the missing methods for `OpenIDCode`:

    from authlib.oidc.core import grants, UserInfo

    class OpenIDCode(grants.OpenIDCode):
        def exists_nonce(self, nonce, request):
            exists = AuthorizationCode.query.filter_by(
                client_id=request.payload.client_id, nonce=nonce
            ).first()
            return bool(exists)

        def get_jwt_config(self, grant):
            return {
                'key': read_private_key_file(key_path),
                'alg': 'RS512',
                'iss': 'https://example.com',
                'exp': 3600
            }

        def generate_user_info(self, user, scope):
            return UserInfo(
                sub=user.id,
                name=user.name,
                email=user.email,
            ).filter(scope)

Second, since there is one more `nonce` value in the `AuthorizationCode` data, we need to save this value into the database. In this case, we have to update our Authorization Code Grant `save_authorization_code` method:

    class AuthorizationCodeGrant(_AuthorizationCodeGrant):
        def save_authorization_code(self, code, request):
            # openid request MAY have "nonce" parameter
            nonce = request.payload.data.get('nonce')
            auth_code = AuthorizationCode(
                code=code,
                client_id=request.client.client_id,
                redirect_uri=request.redirect_uri,
                scope=request.payload.scope,
                user_id=request.user.id,
                nonce=nonce,
            )
            db.session.add(auth_code)
            db.session.commit()
            return auth_code

        # ...

Finally, you can register `AuthorizationCodeGrant` with the `OpenIDCode` extension:

    # register it to grant endpoint
    server.register_grant(AuthorizationCodeGrant, [OpenIDCode(require_nonce=True)])

The difference between OpenID Code flow and the standard code flow is that OpenID Connect requests have a scope of “openid”:

    GET /authorize?
    response_type=code
    &scope=openid%20profile%20email
    &client_id=s6BhdRkqt3
    &state=af0ifjsldkj
    &redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb HTTP/1.1
    Host: server.example.com

With the example above, you will also have to change the scope of your client in your application to something like `openid profile email`.

Now that you added the `openid` scope to your application, an OpenID token will be provided to this app whenever a client asks for a token with an `openid` scope.

## Implicit Flow

The Implicit Flow is mainly used by Clients implemented in a browser using a scripting language. You need to implement the missing methods of `OpenIDImplicitGrant` before registering it:

    from authlib.oidc.core import grants

    class OpenIDImplicitGrant(grants.OpenIDImplicitGrant):
        def exists_nonce(self, nonce, request):
            exists = AuthorizationCode.query.filter_by(
                client_id=request.payload.client_id, nonce=nonce
            ).first()
            return bool(exists)

        def get_jwt_config(self):
            return {
                'key': read_private_key_file(key_path),
                'alg': 'RS512',
                'iss': 'https://example.com',
                'exp': 3600
            }

        def generate_user_info(self, user, scope):
            return UserInfo(
                sub=user.id,
                name=user.name,
                email=user.email,
            ).filter(scope)

    server.register_grant(OpenIDImplicitGrant)

## Hybrid Flow

The Hybrid flow is a mix of code flow and implicit flow. You only need to implement the authorization endpoint part, as token endpoint will be handled by Authorization Code Flow.

OpenIDHybridGrant is a subclass of OpenIDImplicitGrant, so the missing methods are the same, except that OpenIDHybridGrant has one more missing method, that is `save_authorization_code`. You can implement it like this:

    from authlib.oidc.core import grants
    from authlib.common.security import generate_token

    class OpenIDHybridGrant(grants.OpenIDHybridGrant):
        def save_authorization_code(self, code, request):
            nonce = request.payload.data.get('nonce')
            item = AuthorizationCode(
                code=code,
                client_id=request.client.client_id,
                redirect_uri=request.redirect_uri,
                scope=request.payload.scope,
                user_id=request.user.id,
                nonce=nonce,
            )
            db.session.add(item)
            db.session.commit()
            return code

        def exists_nonce(self, nonce, request):
            exists = AuthorizationCode.query.filter_by(
                client_id=request.payload.client_id, nonce=nonce
            ).first()
            return bool(exists)

        def get_jwt_config(self):
            return {
                'key': read_private_key_file(key_path),
                'alg': 'RS512',
                'iss': 'https://example.com',
                'exp': 3600
            }

        def generate_user_info(self, user, scope):
            return UserInfo(
                sub=user.id,
                name=user.name,
                email=user.email,
            ).filter(scope)

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

Since all OpenID Connect Flow require `exists_nonce`, `get_jwt_config` and `generate_user_info` methods, you can create shared functions for them.

Find the example of OpenID Connect server.