I'm implemented a solution which is constituted by a .NET back-end application based on ASP.NET: since the team that I'm considering to build should be composed of me and one or two front-end developers working in PHP.

A good side effect of this architecture is that PHP is a fast server-side scripting engine which require less resources than ASP.NET.

The only solution i've found for allowing the two layers to communicate is through XML-RPC, which is a protocol supported by both the systems (although the back-end part was implemented by me). One problem of this approach is that XML-RPC doesn't support any authentication system and has some lack of performances in the serialization/deserialization between the object notation and the XML representation.

Has anyone any consideration or alternative solution?