Is is possible to configure secured CW browser access using https or ssl certificates?
There are no such things as CS 2.5 and 2.6, so I will assume you mean CS 3.0 for LMS 2.5 and 2.6. For LMS 2.2, you can only enable SSL mode if you do not have DFM installed. To enable SSL mode, go to Server Configuration > Administration > Security Management > Enable/Disable SSL.
For LMS 2.5 and higher, SSL can always be enabled. To do this, go to Common Services > Server > Security > Browser-Server Security Mode Setup.