GetExtensionsAssignedToUser.
        [Preview API] Returns extensions that are currently assigned to the user in the account
        :param str user_id: The user's identity id.
        :rtype: {LicensingSource}

def get_extensions_assigned_to_user(self, user_id):
        """GetExtensionsAssignedToUser.
        [Preview API] Returns extensions that are currently assigned to the user in the account
        :param str user_id: The user's identity id.
        :rtype: {LicensingSource}
        """
        route_values = {}
        if user_id is not None:
            route_values['userId'] = self._serialize.url('user_id', user_id, 'str')
        response = self._send(http_method='GET',
                              location_id='8cec75ea-044f-4245-ab0d-a82dafcc85ea',
                              version='5.0-preview.1',
                              route_values=route_values)
        return self._deserialize('{LicensingSource}', self._unwrap_collection(response))