FOS\UserBundle\Model\UserInterface::setPlainPassword PHP Method

    function setPlainPassword($password);

 /**
  * @param UserInterface $user
  */
 protected function onSuccess(UserInterface $user)
 {
     if ($this->getNewPassword() != "") {
         $user->setPlainPassword($this->getNewPassword());
     }
     $this->userManager->updateUser($user);
 }