as per
https://datatracker.ietf.org/doc/html/rfc2869#section-5.14> This attribute MAY be used to sign Access-Requests
accel-ppp currently doesn't support it as it's allowed (no MUST word)
> A RADIUS Server receiving an Access-Request with a Message-Authenticator Attribute present MUST calculate the correct value of the Message-Authenticator and silently discard the packet if it does not match the value sent.
your radius server violates rfc by required attr to always be present, but not even try to check it