Get HTTP Header information From JavaScript

Note : It's not possible to read the current headers. You could make another request to the same URL and read its headers, but there is no guarantee that the headers are exactly equal to the current.

Create a customizable text.

Example :
use Drupal\Component\Render\FormattableMarkup;
$text = new FormattableMarkup('My name is @name', ['@name' => "The name"]);

Drupal's event system allow to create triggers when an event has been happened like create a custom hook on drupal 7.

Use Event Subscriber service.

The EventSubscriber allow to execute an action on boot as hook_boot or hook_init of drupal 7.

Example.

To force usage of a specific key, put in your ~/.ssh/config file :

Host [HOST_NAME]
   Hostname [HOST_NAME]
   User [USER_NAME]
   Port [PORT]
   IdentityFile ~/.ssh/[your_private_key]