2 servers - frontend + backend: auth + attributes

Hello!
I want to implement next scheme (PAP protocol, FreeRADIUS 3.0.27):
client sends request to frontend server , frontend server authenticates user ,
frontend server sends request to backend server, backend server
authenticates user and adds attributes,
frontend server returns extra attributes to client.
It seems frontend server can proxy request after authorization, so the
part with authentication on frontend server is missed.
Is it possible to implement this approach?

Regards
Andrei
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