Get the authorization URL for your application, given the application's
        client_id, redirect_uri, scope, and optional state data.

def authorize_url(self, client_id, redirect_uri, scope, state=None):
        """Get the authorization URL for your application, given the application's
        client_id, redirect_uri, scope, and optional state data."""
        params = [
            ('client_id', client_id),
            ('redirect_uri', redirect_uri),
            ('scope', scope)
        ]
        if state:
            params.append(('state', state))
        return "%s?%s" % (CreateSend.oauth_uri, urlencode(params))