!!! Overview
[{$pagename}] [Proxy] [Authentication] Required [HTTP Status Code] indicates that the [HTTP Request] has not been applied because it lacks valid [authentication] [credentials] for a [Proxy Server] that is between the [user-agent] and the [server] that can access the requested [resource].

[{$pagename}] is sent with a [Proxy-Authenticate] [HTTP Response Header] that contains information on how perform [Authorization] correctly.

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]