By running it through prove instead of just running it directly, you make it harder to understand the output. But...

            my $ok = eval {
                $c->authenticate(
                    { username => $user, password => $info->{password}
+ },
                ); 
            };
            diag $@;
            diag $ok;
[...]
t/live_app_realms_progressive.t 
t/live_app_realms_progressive.t .. # 
# undef
[...]
# 
# undef
[download]

Shows that the eval is failing (setting $ok to undef) but also leaving $@ as the empty string. Devel::EvalError explains how this can happen -- some of this has changed in the most recent versions of Perl (somewhat for the better, somewhat for the worse).

Devel::EvalError will even add a __DIE__ handler for you so that you can see the lost $@ value. The syntax of that module is stupidly ugly (the author was foolishly thinking that he had to avoid 'try { ... }' syntax because you can't "return" from it when the fact is that you can't "return" from 'eval { ... }' in exactly the same way and what he needed to avoid was only the obnoxious 'catch { ... }' syntax), so you can also just add your own __DIE__ handler simply enough.

Update: Oops. That is only one possible explanation. But it is more likely that the method call is just returning undef. I'd write that as:

    my $res;
    my $ok= eval {
        $res= $c->...;
        1;
    };
[download]

so the distinction is clear.