Harden iFlow proxy requests to match CLI behavior

[redzrush101]

Summary

• Port iFlow CLI-style anti-block request behavior into the iFlow provider used by LLM-API-Key-Proxy.
• Add signed-header handling with a one-shot 406 retry without signature plus upstream API base fallback support.
• Fix env-based OAuth credential loading/refresh handling and include glm-5 in iFlow hardcoded models.

Validation

• Ran compile checks for modified provider files.
• Started proxy with OAuth creds provided via environment variables from oauth_creds.json mapping.
• Verified streaming calls through proxy endpoint for iflow/glm-5 and iflow/kimi-k2.5.

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Important

Enhance iFlow proxy requests to match CLI behavior with improved signed-header handling, OAuth credential management, and API base fallback support.

• Behavior:
  • Port CLI-style anti-block request behavior into iFlow provider in iflow_provider.py.
  • Add signed-header handling with a one-shot 406 retry without signature and upstream API base fallback.
  • Fix OAuth credential loading/refresh from environment variables in iflow_auth_base.py.
• Models:
  • Include glm-5 in hardcoded models in iflow_provider.py.
• Functions:
  • Add get_api_base_candidates() and get_api_base() in iflow_auth_base.py for API base URL management.
  • Modify _refresh_token() in iflow_auth_base.py to handle env-loaded credentials without file IO.
  • Update get_api_details() in iflow_auth_base.py to support env-based credentials.
  • Enhance _build_iflow_headers() in iflow_provider.py to include optional signature headers.
  • Implement _should_fallback_base() in iflow_provider.py for handling specific HTTP status codes.
• Misc:
  • Verify streaming calls for iflow/glm-5 and iflow/kimi-k2.5 through proxy endpoint.

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[Mirrowel]

Gotta give it a couple of days to verify

[redzrush101]

Gotta give it a couple of days to verify

ye good