Merge pull request #18940 from BerriAI/litellm_fix_extra_headers

[fix] forward MCP extra headers case-insensitively

litellm/proxy/_experimental/mcp_server/mcp_server_manager.py

@@ -1825,9 +1825,17 @@ class MCPServerManager:
         if mcp_server.extra_headers and raw_headers:
             if extra_headers is None:
                 extra_headers = {}
+
+            normalized_raw_headers = {
+                str(k).lower(): v for k, v in raw_headers.items() if isinstance(k, str)
+            }
             for header in mcp_server.extra_headers:
-                if isinstance(header, str) and header in raw_headers:
-                    extra_headers[header] = raw_headers[header]
+                if not isinstance(header, str):
+                    continue
+                header_value = normalized_raw_headers.get(header.lower())
+                if header_value is None:
+                    continue
+                extra_headers[header] = header_value
 
         if mcp_server.static_headers:
             if extra_headers is None:

litellm/proxy/_experimental/mcp_server/server.py

@@ -715,9 +715,18 @@ if MCP_AVAILABLE:
         if server.extra_headers and raw_headers:
             if extra_headers is None:
                 extra_headers = {}
+
+            normalized_raw_headers = {
+                str(k).lower(): v for k, v in raw_headers.items() if isinstance(k, str)
+            }
+
             for header in server.extra_headers:
-                if header in raw_headers:
-                    extra_headers[header] = raw_headers[header]
+                if not isinstance(header, str):
+                    continue
+                header_value = normalized_raw_headers.get(header.lower())
+                if header_value is None:
+                    continue
+                extra_headers[header] = header_value
 
         if server_auth_header is None:
             server_auth_header = mcp_auth_header

tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py

@@ -79,6 +79,33 @@ async def test_mcp_server_tool_call_body_contains_request_data():
     assert body["arguments"] == tool_arguments
 
 
+def test_prepare_mcp_server_headers_case_insensitive_extra_headers():
+    try:
+        from litellm.proxy._experimental.mcp_server.server import (
+            _prepare_mcp_server_headers,
+        )
+    except ImportError:
+        pytest.skip("MCP server not available")
+
+    server = MCPServer(
+        server_id="server-case",
+        name="server",
+        transport=MCPTransport.http,
+        extra_headers=["Authorization"],
+    )
+
+    server_auth_header, extra_headers = _prepare_mcp_server_headers(
+        server=server,
+        mcp_server_auth_headers=None,
+        mcp_auth_header=None,
+        oauth2_headers=None,
+        raw_headers={"authorization": "Bearer token"},
+    )
+
+    assert server_auth_header is None
+    assert extra_headers == {"Authorization": "Bearer token"}
+
+
 @pytest.mark.asyncio
 async def test_get_prompts_from_mcp_servers_success():
     try:

tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py

@@ -12,6 +12,7 @@ sys.path.insert(0, "../../../../../")
 import httpx
 from mcp import ReadResourceResult, Resource
 from mcp.types import (
+    CallToolResult,
     GetPromptResult,
     Prompt,
     ResourceTemplate,
@@ -286,6 +287,50 @@ class TestMCPServerManager:
         assert len(result) == 1
         assert result[0].name == "github_tool_1"
 
+    @pytest.mark.asyncio
+    async def test_call_regular_mcp_tool_case_insensitive_extra_headers(self):
+        """_call_regular_mcp_tool should forward headers regardless of original casing."""
+
+        manager = MCPServerManager()
+        server = MCPServer(
+            server_id="server-case-call",
+            name="case-call-server",
+            url="https://example.com",
+            transport=MCPTransport.http,
+            auth_type=MCPAuth.authorization,
+            extra_headers=["Authorization"],
+        )
+
+        mock_client = AsyncMock()
+        mock_client.call_tool = AsyncMock(
+            return_value=CallToolResult(content=[], isError=False)
+        )
+        captured_extra_headers = None
+
+        def capture_create_mcp_client(
+            server, mcp_auth_header, extra_headers, stdio_env
+        ):  # pragma: no cover - helper
+            nonlocal captured_extra_headers
+            captured_extra_headers = extra_headers
+            return mock_client
+
+        manager._create_mcp_client = MagicMock(side_effect=capture_create_mcp_client)
+
+        result = await manager._call_regular_mcp_tool(
+            mcp_server=server,
+            original_tool_name="tool",
+            arguments={},
+            tasks=[],
+            mcp_auth_header=None,
+            mcp_server_auth_headers=None,
+            oauth2_headers=None,
+            raw_headers={"authorization": "Bearer token"},
+            proxy_logging_obj=None,
+        )
+
+        assert captured_extra_headers == {"Authorization": "Bearer token"}
+        assert isinstance(result, CallToolResult)
+
     @pytest.mark.asyncio
     async def test_get_prompts_from_server_success(self):
         """Ensure prompts are fetched and prefixed when requested."""