test(mcp): assert config token via resolved_auth, not the headers dict

test_mcp_server_config_auth_value_header_used inspected _get_auth_headers(), but the
graft now carries the static credential on the client's httpx.Auth (resolved_auth) and
writes the header at send time, so that dict is empty. Assert the header the
StaticHeaderAuth emits onto the request instead. Both config keys (authentication_token,
auth_value) stay covered.

tests/mcp_tests/test_mcp_auth_priority.py

@@ -45,7 +45,18 @@ async def test_mcp_server_works_without_config_auth_value():
 
 @pytest.mark.parametrize("token_key", ["authentication_token", "auth_value"])
 async def test_mcp_server_config_auth_value_header_used(token_key):
-    """Ensure auth header is sent when auth token configured in config"""
+    """Ensure the configured auth token is emitted as the upstream Authorization header.
+
+    The token is resolved through the v2 credential resolver and rides on the client's
+    httpx.Auth, so assert the header it writes onto the request rather than the (now
+    credential-free) _get_auth_headers() dict.
+    """
+    import httpx
+
+    from litellm.proxy._experimental.mcp_server.outbound_credentials.httpx_auth import (
+        StaticHeaderAuth,
+    )
+
     config = {
         "test_server": {
             "url": "https://api.example.com/mcp",
@@ -60,7 +71,8 @@ async def test_mcp_server_config_auth_value_header_used(token_key):
 
     server = next(iter(manager.config_mcp_servers.values()))
     client = await manager._create_mcp_client(server)
-    headers = client._get_auth_headers()
 
-    assert headers["Authorization"] == "Bearer example_token"
+    assert isinstance(client._resolved_auth, StaticHeaderAuth)
+    emitted = next(client._resolved_auth.auth_flow(httpx.Request("POST", server.url)))
+    assert emitted.headers["Authorization"] == "Bearer example_token"
     assert client.auth_type == MCPAuth.bearer_token