Here an exemple : Module name : mymodule

Here an example to get the current page path programmatically in Drupal 8

    $current_url = Url::fromRoute('<current>');
    $path = $current_url->toString();

Exemple : Field 'username'

Store data on session.

Example:

$session = new \Symfony\Component\HttpFoundation\Session\Session();
$session->set('var_name', $session->get('var_name',0) + 1);
drupal_set_message($session->get('var_name'));

The solution is:
ssh-keygen -R <host>

Example:
ssh-keygen -R 127.0.0.1
ssh-keygen -R domainname.com