How to communicate between ASP.Net program and a php opensource program

I need to talk between an extendable piece of ASP.Net software and an opensource PHP software. I need to mirror database tables on each side with information flowing both ways. The information has to be secure and I don’t want just anyone to be able to post information.

I have seen sending information by the POST or GET methods. Wouldn’t this be a security issue cause if someone knew the variable names then they could easily send information themselves?

Also I have read about SOAP and xml-rpc which seem to be quite similar but I haven’t found any conclusive choice whether to go one way or the other.

What about web services isn’t this just a way to transport front end content?

I know I am new to this aspect of web development but I have tons of experience with PHP and a lot of experience with ASP.Net. Any help would be very much appreciated. Thankyou

anyone? perhaps I am missing something obvious here but would really appreciate some help

I’d start with “what is the physical archetecture?”

Mainly because if they co-habit the same box, or something local, you can do alot more.

If the communications need to be over the internet, I’d go with either XML-RPC or a SOAP web service depending on where the heavy lifting is going to happen. From the .NET side of things, check out the Windows Communication Framework, it should let you do what you need.