test(mcp): cover static-prefix issuer discovery

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

@@ -11234,3 +11234,50 @@ def test_named_resource_discovery_follows_matching_authorization_issuer(
     authorization = client.get(f"{prefix}/.well-known/oauth-authorization-server/{issuer_path}")
     assert authorization.status_code == 200
     assert authorization.json()["issuer"] == resource["authorization_servers"][0]
+
+
+def test_static_root_path_authorization_discovery_preserves_issuer(monkeypatch):
+    import subprocess
+    import sys
+
+    monkeypatch.setenv("SERVER_ROOT_PATH", "/gateway")
+    monkeypatch.setenv("PROXY_BASE_URL", "http://testserver/gateway")
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            """
+import json
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from litellm.proxy._experimental.mcp_server.discoverable_endpoints import router
+from litellm.proxy._experimental.mcp_server.mcp_server_manager import global_mcp_server_manager
+from litellm.types.mcp import MCPAuth, MCPTransport
+from litellm.types.mcp_server.mcp_server_manager import MCPServer
+
+global_mcp_server_manager.registry['example'] = MCPServer(
+    server_id='example', name='example', server_name='example', alias='example',
+    transport=MCPTransport.http, auth_type=MCPAuth.oauth2,
+    authorization_url='https://idp.example.com/authorize', token_url='https://idp.example.com/token',
+)
+app = FastAPI(root_path='/gateway')
+app.include_router(router)
+with TestClient(app) as client:
+    responses = {
+        path: client.get('/.well-known/oauth-authorization-server/gateway/' + path)
+        for path in ('mcp/example', 'example/mcp', 'example', 'mcp')
+    }
+    print(json.dumps({path: {'status': response.status_code, 'body': response.json()}
+                      for path, response in responses.items()}))
+""",
+        ],
+        capture_output=True,
+        text=True,
+        check=True,
+        timeout=60,
+    )
+    responses = json.loads(result.stdout)
+    for path in ("mcp/example", "example/mcp", "example", "mcp"):
+        assert responses[path]["status"] == 200, responses[path]
+        assert responses[path]["body"]["issuer"] == f"http://testserver/gateway/{path}"
+    assert responses["example/mcp"]["body"]["token_endpoint"] == "http://testserver/gateway/example/token"