google app engine - UrlFetch with Proxy-Authorization header -

i'm trying make request using urlconnection (implemented on appengine urlfetch of course).

i'm working via proxy server , pass proxy-authorization header in request (java). requests app engine returns 407.

any idea? how supposed work proxy server appengine?

i did little experiment once , looks proxy-authorization header being stripped urlfetch. might correct strip 1 proxy-authorization header urlfetch conforming http/1.1 proxy, if send multiple proxy-authorization headers seem removed. looks bug me.