Authn module

Module asab.web.authn provides middlewares and classes to allow only authorized users access specified web server endpoints. It also allows to forward requests to the authorization server via instance of OAuthForwarder.

Currently available authorization technologies include OAuth 2.0, public/private key and HTTP basic auth.


authn_middleware_factory(app, implementation, *args, **kwargs):

First step is to define the authorization implementation, which can be the OAuth 2.0, public/private key or HTTP basic auth. Depending on the implementation, there are arguments which further specify the authorization servers that are going to be used.

When it comes to OAuth 2.0, there are methods for every OAuth 2.0 server, that is going to be used for authorization and obtainment of the user identity. The relevant method is selected based on access token prefix, that is received from the client in the HTTP request (Authorization header):

Authorization: Bearer <OAUTH-SERVER-ID>-<ACCESS_TOKEN>

The following example illustrates how to register a middleware inside the web server container with OAuth 2.0 implementation and GitHub method.

        "oauth2client",  # other implementations include: "basicauth" and "pubkeyauth"
        # Use GitHub OAuth provider


In order to require authorization for a specific endpoint and thus utilize the output of the registered middleware, it is necessary to decorate its handler method with authn_required_handler decorator.

The decorator provide the handler method with an identity argument, which contains the user identity received from the authorization server. Thus the user information can be further evaluated or included as part of the response. To receive just the identity information but not force the authorization for the endpoint, the authn_optional_handler can be used instead.

The following example illustrates how to use the authn_required_handler decorator in order to enforce the authorization and receive user identity in the identity argument:

async def user(self, request, *, identity):
    return, data={
        'message': '"{}", you have accessed our secured "user" endpoint.'.format(identity),


To see & try the full example which utilizes OAuth 2.0 middleware and decorators, please see the code in the following link:

Another example serves to demonstrate the public/private key authorization via ASAB web client ssl cert authorization: