M13: harden MCP trust boundary

backend/app/api/deps.py

@@ -1,6 +1,9 @@
 from __future__ import annotations
 
+import hmac
+import re
 from collections.abc import Generator
+from dataclasses import dataclass
 
 from fastapi import Depends, Header, HTTPException, Request, status
 from sqlalchemy.orm import Session
@@ -60,12 +63,30 @@ def require_operations_manager(
     return user
 
 
+@dataclass(frozen=True)
+class McpClientContext:
+    client_id: str
+    tenant: str
+
+
+_MCP_CLIENT_ID = re.compile(
+    r"^itworx-mcp-hub:(?:readiness|mobilityops:[A-Za-z0-9][A-Za-z0-9._:-]{0,127})$"
+)
+
+
 def require_mcp_service_token(
     x_service_token: str = Header(..., alias="X-Service-Token"),
-    x_client_id: str = Header(default="unknown-mcp-client", alias="X-Client-Id"),
-) -> str:
-    if x_service_token != settings.mcp_hub_service_token:
+    x_client_id: str = Header(..., alias="X-Client-Id", min_length=1, max_length=180),
+    x_tenant_id: str | None = Header(default=None, alias="X-Tenant-Id", max_length=120),
+) -> McpClientContext:
+    if not hmac.compare_digest(x_service_token, settings.mcp_hub_service_token):
         raise HTTPException(
             status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid service token"
         )
-    return x_client_id
+    if not _MCP_CLIENT_ID.fullmatch(x_client_id):
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN, detail="Untrusted MCP client identity"
+        )
+    if x_tenant_id is not None and x_tenant_id != settings.ragcore_tenant:
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Tenant mismatch")
+    return McpClientContext(client_id=x_client_id, tenant=settings.ragcore_tenant)