Does GAE/OpenID/OAuth support xmlhttp proxy?

Currently, my code would construct the GWT form, which user would submit directly to openId (or any authenticaiton service). Such a method works fine.

However, what if I had the gwt page server access the 开发者_如何学运维OpenID provider, is there a way/strategy for the server to mediate authentication between its client and the auth provider?

I wish to know the answers with respect to

• GAE as the proxy

and, regardless if GAE or Tomcat is the intended proxy, answers wrt

• Google Accounts
• OpenID
• OAuth

If so, it would be wonderful if someone could describe the installation strategy.