The note behind is not helpfull?

Support for sessions - this is necessary, for example, for the access to Locked Pages.

So this means that if a customer needs to give mailadress and pasword, acces will be given if correct pffcource, so acces with credentials will work properly. 

Thanks for reply. That tells me the application, but not what settings are required on the server with the hosting company.

----- translated from a German Webseite -----

Sessions are another method of exposing data from one site to another site (of the same domain). When a visitor accesses a website, the server assigns them a unique ID (called a session ID or SID).

This is either stored in a cookie (named PHPSESSID) on the user's computer or passed in the URL (if the browser does not accept cookies). Based on this SID a unique session data file is created on the server, stored in a directory as specified by the session.save_path in the php.ini file.

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