<?

class AuthenticationHelper extends Singleton {

  private $data = [];

  function setParameter(string $key, ?$value) {
    // no type checking
    // value as the name is too generic
    // Since SOME parameters might be null
    // You cannot check a single parameter for not null

    $this->data[$key] = value;
  }

  function getParameter(string $key) {
    // no return type hinting
    return $this->data[$key] ?? null;
  }

}

// Usages

AuthenticationHelper::getInstance->setParameter('oauth2_token', []);
// type error not caught

AuthenticationHelper::getInstance->setParameter('scopes', null);
// We need to enforce this not to be NULL

AuthenticationHelper::getInstance->setParameter('user', 'Elon');
// This should not mutate
// No validation with business rules

$credential = AuthenticationHelper::getInstance->getParameter('oauth2token');
// Typo not detected

// You can not easily find references to methods setting the oauth2_token

<?

class AuthenticationCredentials {

  private $user;
  private $oauth2_token;

  function __construct(User $user) {
    $this->validateUser($user);
    // Specific validation rules

    $this->user = $user;
    // Cannot mutate 
  }

  function oauth2_token(string $token): void {
    // You can add specific validations
    $this->oauth2_token = $token;
  }

  function oauth2_token(): string {    
    // Return type hinting
    return $this->oauth2_token;
  }

}

// Usages

$credentials = new AuthenticationCredentials(new User('Elon'));
// Valid since creation

$credentials->oauth2_token([]);
// type errors are caught

$credentials->oauth2_token(null);
// cannot be null. Fail fast

$credentials->scope();
// Typo detected