[middleware] convert acl_middleware function to class

halfapi/lib/acl_middleware.py

@@ -1,8 +1,10 @@
 #!/usr/bin/env python3
 from starlette.requests import Request
 from starlette.exceptions import HTTPException
+from starlette.middleware.base import BaseHTTPMiddleware
 
-async def acl_middleware(request: Request, call_next):
+class AclMiddleware(BaseHTTPMiddleware):
+    async def dispatch(self, request: Request, call_next):
         """ Checks the "acls" key in the scope and applies the
             corresponding functions in the current module's acl lib.