Custom headers do not REQUIRE a prefix. So the lack of prefix does not make it non-compliant. In fact, the HTTP RFC doesn't even say they SHOULD have a prefix. And RFC822 which defines headers only says that protocol mandated headers MUST NOT be prefixed with "X-". Also, there's a draft proposal to deprecate the "X-" header prefix as it does more harm than good: http://tools.ietf.org/html/draft-ietf-appsawg-xdash-02
Also, the top line should read POST rest/getAuthID.aspx HTTP/1.1
Correction: Use of "X-" has been depreciated in a draft resolution.
Edit: As mentioned below, it isn't compliant in its use of the verbs (GET/POST etc).