SAML single log out implementation

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PHP

Here is something I need to implement:
When a user clicks on "logout" button on xyz.com,
Xyz.com is the Identity provider who sends a SAML <logout request=""> to abc.com (service provider.
Now abc.com has to kill the user session and send back SAML <logout response=""> to IDP.

I need some1 to help me out with the steps involved in this entore SAML SLO Process.
Also, what is the use of a X509 certificate,etc..

I am completely clueless how this works.


Help me ! someone