Commit 3753970cc9 widened the Authorization strip to cover all
is_oauth_passthrough servers — protecting against the LiteLLM admission
key leaking upstream when the caller used Authorization for admission,
but also silently stripping legitimate upstream OAuth bearers when the
caller used x-litellm-api-key for admission.
That broke transparent OAuth pass-through (EAI-506 V5/V6): standards-
compliant MCP clients (OpenCode, Claude Code, mcp-inspector) complete
PKCE against the upstream IdP and send the resulting token as plain
Authorization: Bearer per the MCP spec — with the wider strip in place,
that token never reaches the upstream and tools/list returns empty.
Narrow the strip: skip Authorization for pass-through servers only when
the caller did NOT supply x-litellm-api-key. When x-litellm-api-key is
present, admission is unambiguous and Authorization is free to carry
the upstream OAuth bearer.
The original security guarantee is preserved — a client that sends only
Authorization (no x-litellm-api-key) still has it stripped, so the
LiteLLM key cannot leak upstream via that path.
Tests:
- new: forwards Authorization when x-litellm-api-key is present
- new: still strips Authorization when only Authorization is present
- existing pass-through + M2M tests unchanged
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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