UpdateUser.
        [Preview API] Map an existing user to a different identity
        :param :class:`<GraphUserUpdateContext> <azure.devops.v5_1.graph.models.GraphUserUpdateContext>` update_context: The subset of the full graph user used to uniquely find the graph subject in an external provider.
        :param str user_descriptor: the descriptor of the user to update
        :rtype: :class:`<GraphUser> <azure.devops.v5_1.graph.models.GraphUser>`

def update_user(self, update_context, user_descriptor):
        """UpdateUser.
        [Preview API] Map an existing user to a different identity
        :param :class:`<GraphUserUpdateContext> <azure.devops.v5_1.graph.models.GraphUserUpdateContext>` update_context: The subset of the full graph user used to uniquely find the graph subject in an external provider.
        :param str user_descriptor: the descriptor of the user to update
        :rtype: :class:`<GraphUser> <azure.devops.v5_1.graph.models.GraphUser>`
        """
        route_values = {}
        if user_descriptor is not None:
            route_values['userDescriptor'] = self._serialize.url('user_descriptor', user_descriptor, 'str')
        content = self._serialize.body(update_context, 'GraphUserUpdateContext')
        response = self._send(http_method='PATCH',
                              location_id='005e26ec-6b77-4e4f-a986-b3827bf241f5',
                              version='5.1-preview.1',
                              route_values=route_values,
                              content=content)
        return self._deserialize('GraphUser', response)