Work around for iFrame cross domain policy?

I have an iFrame and, understandably, I can't edit the elements.

Is there a work around for this, like using some sort o开发者_运维知识库f proxy? I would need it to work for any website and have things like sessions and cookie data persist (for logins etc).

Is it at all possible?

Nup, and you can't use CORS because it is only supported by XHR.

Same Origin Policy is going to stop you, and rightfully so.

If you could proxy the site through your own domain, protocol and port, it'd work, but that is often quite difficult.