<form action="/admin/index.php?action=login" method="post" name="action"> 
   <input type="hidden" name="ADMIN" value="f23af307ea00b284fb9e74c4cbabfbdf" /> 
   <input type="text" name="username" size="12" value=""> 
   <input type="password" name="password" size="12"> 
   <input type="submit" name="login" value="Login"> 
</form> 

use WWW::Mechanize; 
use LWP::Debug qw(+); 

$username = "xxx"; 
$password = "xxx"; 

my $mech = WWW::Mechanize->new(); 

   $mech->cookie_jar(HTTP::Cookies->new()); 
   $mech->get( "https://meineSeite.de/admin" ); 
    
   #Get ADMIN-ID 
   $mech->content() =~ /name=\"ADMIN\" value=\"([^\"]+)/g; 
   $hiddenField = $1; 
       
   #Fill form 
   $mech->submit_form( 
                 form_name => "action", 
                   fields      => { 
                     ADMIN => $hiddenField, 
                     username   => $username, 
                     password => $password}, 
                   button => 'login'); 

    #Print site            
   print $mech->content(); 
 

LWP::UserAgent::new: () 
LWP::UserAgent::request: () 
HTTP::Cookies::add_cookie_header: Checking <<URL>> for cookies 
LWP::UserAgent::send_request: GET https://meineSeite/admin 
LWP::UserAgent::_need_proxy: Not proxied 
LWP::Protocol::http::request: () 
LWP::Protocol::collect: read 242 bytes 
LWP::UserAgent::request: Simple response: Moved Permanently 
LWP::UserAgent::request: () 
HTTP::Cookies::add_cookie_header: Checking <<URL>> for cookies 
LWP::UserAgent::send_request: GET https://meineSeite/admin 
LWP::UserAgent::_need_proxy: Not proxied 
LWP::Protocol::http::request: () 
LWP::Protocol::collect: read 4096 bytes 
LWP::Protocol::collect: read 965 bytes 
HTTP::Cookies::extract_cookies: Set cookie ADMIN => 829052f0173388362a649d8fe980081b 
LWP::UserAgent::request: Simple response: OK 
LWP::UserAgent::request: () 
HTTP::Cookies::add_cookie_header: Checking <<URL>> for cookies 
HTTP::Cookies::add_cookie_header: - checking cookie path=/ 
HTTP::Cookies::add_cookie_header:  - checking cookie ADMIN=829052f0173388362a649d8fe980081b 
HTTP::Cookies::add_cookie_header:    it's a match 
HTTP::Cookies::add_cookie_header: Checking <<URL>> for cookies 
LWP::UserAgent::send_request: POST https://meineSeite/admin/index.php?action=login 
LWP::UserAgent::_need_proxy: Not proxied 
LWP::Protocol::http::request: () 
LWP::Protocol::collect: read 238 bytes 
LWP::Protocol::collect: read 540 bytes 
LWP::Protocol::collect: read 2348 bytes 
LWP::Protocol::collect: read 219 bytes 
LWP::Protocol::collect: read 419 bytes 
LWP::Protocol::collect: read 160 bytes 
LWP::Protocol::collect: read 1122 bytes 
LWP::UserAgent::request: Simple response: OK