atScanUser scans the given string userName and tries to
derive an AtFS user identification (resultUser) from it.
It does not verify the existence of a corresponding UNIX
(/etc/passwd) user entry. Use atUserUid to test that. atScanUser
understands the following formats:
user
When the string does not contain an at sign, it is considered to be a
plain user name from the current host and domain.
This format can only be recognized, when the given domain is equal to
the current domain, and the hostname remains as rest between the
at sign and domain name.
An user identification string with a domain name different to the
local domain is treated as user@domain, although this might be wrong.
atUserName returns a string of the form user@domain
generated from the given user structure. If no domain name is
given in the structure, it returns user@host instead. With no
host and no domain name, just user is returned. The result
string resides in static memory and will be overwritten on subsequent
calls.
atUserUid tries to map the given user structure to a UNIX
user identification. It returns the uid on success, -1 otherwise.
atUserValid checks the given user structure for
plausibility. It returns FALSE on fauilure, a non null value on
success.