developing a codeigniter soa (services oriented architecture) project: solution? WSDL?

[eluser]Unknown[/eluser]
hi all, i'm new to this forum. I like developing with CI and now i'm in front of a new kind of project.
I'm in the following scenario:

I have to develop a web app that expose gui and methods to another server.

My server = SA
The other server = SB

SB has a login system in which every user can use the methods that SA expose.
how can i allow the SB to see and use the gui that SA expose?
Have i to use WSDL protocol?

thanks in advance.

p.s. i'm italian, sorry for my english.