8 – How to get current user jwt token?

In a custom module, I need to get the jwt token (access_token) related to the current user. Following this issue I’ve tried to get it, but without success, because get_jwt_key() and jwt_token_params() are not defined and I can’t find where they are defined:

use FirebaseJWTJWT;
...    
public function getAccessToken() {
  $uid = Drupal::currentUser()->id();
  // Add JWT access_token
  $key = get_jwt_key(); //key for generate jwt token
  $token = jwt_token_params($uid); // parameters to be added in token.
  $access_token = JWT::encode($token, $key);
  return $access_token;
}

I’ve tried only with:

$access_token = $this->jwtAuth->generateToken();

But I haven’t found how to initialize $jwtAuth service to generate the token.
Any suggestion?