feat(s3): support credential-scoped endpoint and OSS storage provider

[benflexcompute]

Summary

• Add endpoint and storageProvider fields to _UserCredential, letting the STS response redirect the S3 client to a non-AWS backend.
• When storageProvider == OSS, disable AWS integrity-check headers and switch to virtual-hosted addressing; preserves existing path-style behavior for other S3-compatible stores (s3proxy, MinIO) via Env.current.s3_endpoint_url.
• Apply user_credential.endpoint to the boto3 client; Env.current.s3_endpoint_url still takes precedence when set.

Test plan

• Default AWS flow (no storageProvider, no endpoint) still builds client unchanged.
• storageProvider=OSS path: virtual-hosted addressing + checksums disabled.
• S3-compatible dev path (Env.current.s3_endpoint_url set, no storageProvider): path-style + checksums disabled.
• user_credential.endpoint set: client uses that endpoint_url.

🤖 Generated with Claude Code

---

Note

Medium Risk
Medium risk because it changes how the boto3 S3 client is configured (endpoint selection, checksum behavior, and addressing style), which can impact all uploads/downloads and compatibility with different S3 backends.

Overview
Adds optional endpoint and storageProvider fields to the STS userCredentials payload (_UserCredential) and threads them into S3 client construction.

When storageProvider is OSS, the client now disables AWS checksum/integrity behavior and switches to virtual-hosted bucket addressing; other S3-compatible endpoints configured via Env.current.s3_endpoint_url keep the existing path-style + checksum-disabled behavior.

If a credential-scoped endpoint is provided, it is used as the boto3 endpoint_url unless Env.current.s3_endpoint_url is set (which still overrides).

^{Reviewed by Cursor Bugbot for commit 26fc6aa. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

Coverage report (flow360)

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
flow360/cloud
s3_utils.py					154-164, 187-191
Project Total

This report was generated by python-coverage-comment-action