While there are aspects of your Perl that I'd recommend changing to a more modern style, the cause of the problem doesn't spring out at me. I'd suggest putting some extra diagnostics in the loop that might help you see what's happening:

#   next if $username ne $user;
    if ($username ne $user) {
        print "<P>user '$user' didn't match '$username'</P>";
        next;
    }
#   $good = 1 if $username eq $user and $password eq $pass;
    print "<P>matched username '$user'</P>";
    if ($password eq $pass) {
        print "<P>.. and matched password, marking as good</P>";
        $good = 1;
    } else {
        print "<P>.. but password '$pass' didn't match '$password'</P>
+";
    }
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