Xrootd S3 Gateway for WLCG Storage

The Xrootd S3 Gateway is a universal high performance proxy service that can be used to access S3 portals using existing HEP credentials (e.g. JSON Web Tokens and x509). This eliminates one of the biggest roadblocks to using public cloud storage resources. This paper describes how the S3 Gateway leverages existing HEP software (e.g. Davix and XRootD) to provide a familiar scalable service that works with public (i.e. AWS, GCS, etc) and private (i.e. CEPH, MinIO, etc.) S3 portal available to the HEP community, and to seamlessly integrate them into the WLCG storage and data transfer ecosystem. The test was conducted at an ATLAS site and ATLAS installation in GCP and AWS.