how to find the module of a specific function?

rumpumpel1 has asked for the wisdom of the Perl Monks concerning the following question:

let's look at the following code:

use TeamForge6;
my $ctf = TeamForge6->new(proxy => 'http://forge.mysite.org',);
my $session = $ctf->login($userid, $passwd);
[download]

how can I systematically find the module, in which the login function appears?