Squid: The Definitive Guide

HTTP (RFC 2616) allows clients and servers to use their own extension methods . If requests with nonstandard HTTP methods go through Squid, the client receives an "Invalid Request" error message. Squid also writes a cache.log entry, such as this:

2003/09/29 13:40:24 parseHttpRequest: Unsupported method 'XGET'

If you want Squid to accept such requests, you must tell it about the nonstandard methods by listing them after the extension_methods directive.