Basic working example of a PHP based webservice

I need a working example of a Php webservice It needs to include a secure authentication method I need basic documentation on these parts How to configure the sample / db connection How to build the receiving part of the service How to request item from db based on parameters in How to build the response as xml How to consume the response What I want is put this sample on my host and learn from it, google offers a lot but as a starter in PHP i don't know the good practices or shortcuts where it comes to LAMP based solutions. Thanks Brian