Authlib checks returning true

[quaxsze]

In the OAuth2Client class, the checks uses by Authlib on the grant type and response type always return True. We should implement them as following:

    def check_response_type(self, response_type):
        return response_type in self.response_types

    def check_grant_type(self, grant_type):
        return grant_type in self.grant_types

Creating a client as following:

    OAuth2Client.objects.create(
        name='test-client',
        owner=UserFactory(),
        redirect_uris=['https://test.org/callback'],
        grant_types=['authorization_code', 'client_credentials', 'refresh_token', 'password'],
        response_types=['code'],
        **kwargs
    )

The drawback is that it would require a migration for the existing OAuth clients.