package Myapp::Controller::Login;
use Mojo::Base 'Mojolicious::Controller';
sub nolog {
  my $c = shift;
  $c->session(userid => 1);
  $c->redirect_to('menu');
}
1;
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%= form_for nolog => (method => 'POST') => begin
  <p>
  % if (param 'user') {
    <b>Erreur dans le mot de passe ou le nom d'utilisateur. Veuillez r
+éessayer</b><br>
  % }
  Utilisateur :<br>
  %= text_field 'user'
  <br>Mot de passe :<br>
  %= password_field 'pass'
  <br>
  %= submit_button 'Login'
  </p>
% end
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<p>
...
</p>
[download]

Does Class "MyApp::Controller::Login" is not a controller mean anything to you?

Very good spot by Anonymous Monk!

Most likely you are on Windows, or on a case-insensitive file system. That way, Perl loads a file Myapp/Controller/Login.pm even if you ask for MyApp/Controller/Login.pm (note the capital "A" in MyApp). Perl itself remains case-sensitive and looks for a class MyApp::Controller::Login, but your module only declares Myapp::Controller::Login with a lowercase "a".

In the part of your setup that you haven't shown, you are mixing up Myapp and MyApp. Correct that and maybe things work differently.

Mm, no sorry, I do not know why you refer to MyApp. My application is Myapp. I am on linux which is case sensitive.
Sorry, my problem is not so simple...