[dev] horde user authentication via php

[Mehmet Akif]

Hi. I'm new to all this mailing lists and horde stuff. So excuse me if i do something wrong.

im trying to add a new contact to an authenticated account via a web service. 
i'll give all neccessary info to the service such as user id, pass and new contact info. 
and the service should authenticate the user first, then using turba it should add the contact. 
so my question is how to authenticate a user through php?
any help would be great. Thanks in advance.