MVC :: Reverse Proxy And Authentication?

We have nearly completed an ASP.NET MVC web application running with SSL in IIS and now find that we must integrate with a third-party product that is supplied as a PHP web app running under lightppd on an alternate port, but still on the same server.

We want to make the integration appear as seamless as possible, so our initial strategy is to do all of the authentication through our application, implement a reverse proxy to expose selected features from the third-party product, and then set-up the third-party product to only be accessible from localhost and (if we can manage it) only from the user our app pool runs as. As a second layer on top of this, we plan on running the third party active content in an IFRAME, so we can surround it with our menus and headers. With the right fonts and colors, hopefully, it won't look grossly out of place.

First question: Is this strategy totally naive? Given the hand we've been dealt, is there a better one?

Second question: What is the best way to implement the reverse proxy? I was thinking of using a routing rule with an Http Handler that invokes our usual authorization just as a controller would and makes the requests to the other site, streaming out the results it receives. Is there something that already does this generically, that I can just hook up and invoke? Maybe some way to specify a controller to handle everything I need to proxy and then use a ViewResult that represents a call to an external URL I construct from the URL I received?

If I can get a few pointers on what to look for, I can trot off to the docs for the details.