Using the "change password" feature of pam_sss modules always lead to a
bad situation where AD password and Gassi password are not synchronyzed
anymore. To avoid this, we disable the feature in SSSD configuration.
The network password can still be changed using the command `kpasswd`
provided by package `krb5-user`.
I would have preferred something shorter like "trespassers will be shot",
but it seems that it is better to quote an article of the criminal code.
Note: the text of the banner is automatically wrapped by GDM, the use
of line breaks is not required.
