public function attempting($callback)
    {
        if (isset($this->events)) {
            $this->events->listen(Events\Attempting::class, $callback);
        }
    }
public function attempting($callback)
    {
        if (isset($this->events)) {
            $this->events->listen(Events\Attempting::class, $callback);
        }
    }
public function attempting ( $ callback ) { if ( isset ( $ this -> events ) ) { $ this -> events -> listen ( Events \ Attempting :: class , $ callback ) ; } }
Register an authentication attempt event listener.

@param  mixed  $callback
@return void
Register an authentication attempt event listener .