See super class method satosa.backends.base#start_auth
        :type context: satosa.context.Context
        :type request_info: satosa.internal.InternalData

def start_auth(self, context, request_info):
        """
        See super class method satosa.backends.base#start_auth
        :type context: satosa.context.Context
        :type request_info: satosa.internal.InternalData
        """
        oidc_nonce = rndstr()
        oidc_state = rndstr()
        state_data = {
            NONCE_KEY: oidc_nonce,
            STATE_KEY: oidc_state
        }
        context.state[self.name] = state_data

        args = {
            "scope": self.config["client"]["auth_req_params"]["scope"],
            "response_type": self.config["client"]["auth_req_params"]["response_type"],
            "client_id": self.client.client_id,
            "redirect_uri": self.client.registration_response["redirect_uris"][0],
            "state": oidc_state,
            "nonce": oidc_nonce
        }
        args.update(self.config["client"]["auth_req_params"])
        auth_req = self.client.construct_AuthorizationRequest(request_args=args)
        login_url = auth_req.request(self.client.authorization_endpoint)
        return Redirect(login_url)