index.php

<?php

interface ClientInterface{
// mentods
  public link():string;
}

class ClientServer1 implements ClientInterface{
  
  
}

class ClientServer2 implements ClientInterface{
 
}

class Auth {
 
  private $client;
  
  public function __construct (ClientInterface $client){
    $this->client = $client;
    
  }
  
}