The documentation on the S3 API of Ceph RGW is provided at: https://docs.ceph.com/en/latest/radosgw/s3/#radosgw-s3
The documentation on the Swift API of Ceph RGW is provided at: https://docs.ceph.com/en/latest/radosgw/swift/#radosgw-swift
The keystone API is described at: https://developer.openstack.org/api-ref/identity/v3/index.html