From 364e466210a92cae9f60acf605a7257698b5f9d3 Mon Sep 17 00:00:00 2001
From: Joshua Valluru <326636767+joshua-berri@users.noreply.github.com>
Date: Sat, 12 Sep 2026 17:18:54 -0700
Subject: [PATCH] fix(mcp): strip duplicate delegated credentials

---
 .../mcp_server/mcp_server_manager.py          | 14 ++++-----
 .../mcp_server/test_mcp_server.py             | 30 +++++++++++++++++++
 .../mcp_server/test_mcp_server_manager.py     | 23 ++++++++++++++
 3 files changed, 59 insertions(+), 8 deletions(-)

diff --git a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
index d186b4178b4..fb0c623473a 100644
--- a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
+++ b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
@@ -1083,7 +1083,9 @@ def _should_strip_caller_authorization(
 
     has_explicit_litellm_admission_header: Final = _has_explicit_litellm_admission_header(raw_headers)
     if is_delegated_oauth:
-        return not has_explicit_litellm_admission_header
+        return not has_explicit_litellm_admission_header or _authorization_is_litellm_admission_credential(
+            raw_headers, user_api_key_auth
+        )
     return _authorization_is_litellm_admission_credential(raw_headers, user_api_key_auth) or (
         user_api_key_auth is None and not has_explicit_litellm_admission_header
     )
@@ -1110,15 +1112,11 @@ def _authorization_is_litellm_admission_credential(
     That is the case when no usable ``x-litellm-api-key`` was sent, or when the client repeated the
     same key in both headers.
     """
-    if user_api_key_auth is None or not user_api_key_auth.api_key:
-        return False
     admission_header: Final = _raw_header_value(raw_headers, "x-litellm-api-key")
-    if not admission_header:
-        return True
     authorization: Final = _raw_header_value(raw_headers, "authorization")
-    return authorization is not None and strip_auth_scheme(authorization, "Bearer") == strip_auth_scheme(
-        admission_header, "Bearer"
-    )
+    if admission_header and authorization:
+        return strip_auth_scheme(authorization, "Bearer") == strip_auth_scheme(admission_header, "Bearer")
+    return bool(user_api_key_auth and user_api_key_auth.api_key and not admission_header)
 
 
 def _format_byok_openapi_auth_header(mcp_server: MCPServer, mcp_auth_header: str) -> str:
diff --git a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py
index 7dbf49788a0..f5e4a420496 100644
--- a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py
+++ b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py
@@ -578,6 +578,36 @@ def test_prepare_mcp_server_headers_legacy_delegate_preserves_separate_upstream_
     assert extra_headers == {"Authorization": "Bearer upstream-token"}
 
 
+def test_prepare_mcp_server_headers_legacy_delegate_strips_repeated_admission_key():
+    from litellm.proxy._experimental.mcp_server.server import (
+        _prepare_mcp_server_headers,
+    )
+    from litellm.proxy._types import UserAPIKeyAuth
+
+    server = MCPServer(
+        server_id="legacy-delegate-repeated-key",
+        name="legacy-delegate",
+        transport=MCPTransport.http,
+        auth_type=MCPAuth.oauth2,
+        delegate_auth_to_upstream=True,
+    )
+
+    server_auth_header, extra_headers = _prepare_mcp_server_headers(
+        server=server,
+        mcp_server_auth_headers=None,
+        mcp_auth_header=None,
+        oauth2_headers={"Authorization": "Bearer sk-litellm-key"},
+        raw_headers={
+            "x-litellm-api-key": "Bearer sk-litellm-key",
+            "authorization": "Bearer sk-litellm-key",
+        },
+        user_api_key_auth=UserAPIKeyAuth(api_key="sk-litellm-key"),
+    )
+
+    assert server_auth_header is None
+    assert extra_headers is None
+
+
 def test_prepare_mcp_server_headers_m2m_skips_authorization_from_raw_extra_headers():
     """M2M must not merge caller Authorization from raw_headers when extra_headers lists it."""
     try:
diff --git a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
index dc4d7721190..3ccb388116b 100644
--- a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
+++ b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
@@ -3433,6 +3433,29 @@ class TestMCPServerManager:
         )
         assert extra_headers == {"Authorization": "Bearer upstream-token"}
 
+    @pytest.mark.asyncio
+    async def test_call_regular_mcp_tool_legacy_delegate_strips_repeated_admission_key(self):
+        from litellm.proxy._types import UserAPIKeyAuth
+
+        server = MCPServer(
+            server_id="server-legacy-delegate-repeated-key",
+            name="legacy-delegate",
+            url="https://example.com",
+            transport=MCPTransport.http,
+            auth_type=MCPAuth.oauth2,
+            delegate_auth_to_upstream=True,
+        )
+        extra_headers = await self._capture_call_extra_headers(
+            server,
+            oauth2_headers={"Authorization": "Bearer sk-litellm-key"},
+            raw_headers={
+                "x-litellm-api-key": "Bearer sk-litellm-key",
+                "authorization": "Bearer sk-litellm-key",
+            },
+            user_api_key_auth=UserAPIKeyAuth(api_key="sk-litellm-key"),
+        )
+        assert not extra_headers or "authorization" not in {k.lower() for k in extra_headers}
+
     def test_should_strip_caller_authorization_new_modes(self):
         from litellm.proxy._types import UserAPIKeyAuth