entermix

class MyClass
{
    private $a;
    private $b;
    private $c;
    
    public function __construct($a)
    {
        $this->setA($a);
    }
    
    public function setA($a){
        // ... фильтры
        $this->a = $a;
        return $this;
    }
    
    public function getA($a){
        return $this->a;
    }
}

$x = new MyClass($_POST['a']);

$a = "!aHR0cHM6Ly93d3cuYXZ0b3Zva3phbHkucnUvcmFzcGlzYW5pZS9tb3NrdmEvc2NoZWxrb3Zv";

echo base64_decode($a); //https://www.avtovokzaly.ru/raspisanie/moskva/schelkovo