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.
extension_methods XGET XPOST