identity metadata token.
        :type allow_gce_inference: bool
        :param bound_zones: <gce only> The list of zones that a GCE instance must belong to in order to be
            authenticated. If bound_instance_groups is provided, it is assumed to be a zonal group and the group must
            belong to this zone.
        :type bound_zones: list
        :param bound_regions: <gce only> The list of regions that a GCE instance must belong to in order to be
            authenticated. If bound_instance_groups is provided, it is assumed to be a regional group and the group
            must belong to this region. If bound_zones are provided, this attribute is ignored.
        :type bound_regions: list
        :param bound_instance_groups: <gce only> The instance groups that an authorized instance must belong to in
            order to be authenticated. If specified, either bound_zones or bound_regions must be set too.
        :type bound_instance_groups: list
        :param bound_labels: <gce only> A list of GCP labels formatted as "key:value" strings that must be set on
            authorized GCE instances. Because GCP labels are not currently ACL'd, we recommend that this be used in
            conjunction with other restrictions.
        :type bound_labels: list
        :param mount_point: The "path" the method/backend was mounted on.
        :type mount_point: str | unicode
        :return: The data key from the JSON response of the request.
        :rtype: requests.Response
        N)