How to use SOAP / HTTP POST to authenticate user in CI?

Hello,

I am creating a web application using CI for the first time. Also, I've never worked with web services before. I have a read about that in the last days but I still can't make it work according to my need.

I have access to a page like that: http://www.w3schools.com/webservices/tem...tToCelsius but for authenticating employees at my company.
I need to verify their credentials and load a new page based on their rights to access the system.

The only that I did so far was to generate an xml file using the method "POST" through the sign in HTML form. I don't know what to after that.

I installed nuSoap library but every tutorial that I try to follow doesn't seem to be related to what I need.
I can't find good documentation that helps use the classes built in into nuSoap and I can't find good examples of authentication pages using webservices developed in codeIgniter.

Do I need to create a SOAP server/client?

I am completely lost to be honest.

Thank you.