In RFC3261 #11:
The target of the OPTIONS request is identified by the Request-URI, which could identify another UA or a SIP server. If the OPTIONS is addressed to a proxy server, the Request-URI is set without a user part, similar to the way a Request-URI is set for a REGISTER request.
Currently OPTIONS-Pings get an 401 Unauthorized when the userpart is skipped (which is fine with RFC).
Is there a way to modify this behaviour in Asterisk 13+?