A good solution for ASP.NET <-> PHP remoting?

I'm about to start a project that requires an ASP.NET application 开发者_如何学JAVA(MVC 2) to talk to a PHP application (on a different server but I have control over them both). Any ideas of a modern, elegant solution of doing that?

Edit: Authentication would be nice to include in the solution.

Edit 2: Communication is not frequent, once in a while one of the apps have some data changes that it should share with the other.

You can use XMPP if you can modify both applications:

Get Started Here:

http://en.wikipedia.org/wiki/Extensible_Messaging_and_Presence_Protocol