I'm not sure about all the rest, but one old fashioned way to split this cookie that you take is like that: (although I encourage you to use CGI.pm)

my $cookie = $ENV{'HTTP_COOKIE'}; # if you wanna do this like that.
@all = split(/\;/, $cookie);
foreach (@all) {
    ($var, $value) = split(/=/);
    $values{$var} = $value;
}
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now you have a has called %values, from which you can call the username/password :

my $username = $values{'username'};
my $password = $values{'password'};
# now do whatever you want with them.
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not sure why you're doing this like that though..