Cloud Storage S3-compatible XML API

Quake AI concept: S3 Compatibility

• GCP Cloud Storage has an S3-compatible XML API at storage.googleapis.com; auth uses HMAC keys generated separately from GCP service account credentials. Quake AI uses EC2-style credentials (access key + secret) generated via Keystone POST /v3/users/{user_id}/credentials/OS-EC2.
• GCP S3 XML API endpoint is storage.googleapis.com (path-style); Quake AI endpoint is provider-specific. GCP does not support S3 multipart upload via the XML API — the GCS resumable upload API must be used instead. Quake AI's Swift s3api supports S3 multipart upload.
• IAM policies on GCS buckets cannot be managed via S3 ACL API calls through the compatibility layer; bucket IAM must be managed via GCP-native tooling (gcloud, Resource Manager API).
• GCP HMAC keys inherit all permissions of the associated service account with no ability to restrict to a subset of operations. Keystone EC2 credentials inherit the Keystone role of the user who creates them.