Proste pobranie danych z pliku - problem. Opcje

[kggsm]

Witam.
Mam kod jak poniżej. Kiedy wprowadzę w zmienną refreshtoken ręcznie np: 'refreshtoken' => 'abc' wszystko jest ok. Ale jeśli 'refreshtoken' => $plik wywala błąd:

Kod

[Fatal error: Constant expression contains invalid operations in /webapi/oauth.php on line 10

Plik zawiera zwykły ciąg znaków.
Dlaczego i jak to poprawić?
Kod skryptu:

[PHP] pobierz, plaintext 
<?php
/**
 * @author AlleREST.pl
 * @link <a href="http://allerest.pl/logowanie-do-allegro-rest-api/" target="_blank">http://allerest.pl/logowanie-do-allegro-rest-api/</a>
 */
$plik = file_get_contents('./.verkey', FILE_USE_INCLUDE_PATH);
echo 'Twój Refresh Token: ' . $plik . '';
class AllegroOAuth2Client {
 
  protected $providerSettings = [
    'ClientId' => 'xxx',
    'ClientSecret' => 'aaa',
    'ApiKey' => 'bbb',
    'RedirectUri' => 'ccc',
 
    'AuthorizationUri' => 'https://allegro.pl/auth/oauth/authorize',
    'TokenUri' => 'https://allegro.pl/auth/oauth/token',
    'refreshtoken' => $plik
  ];
  protected $headers = [
    'Content-Type: application/x-www-form-urlencoded'
  ];
 
  public function __construct(array $customSettings = []) {
    $this->providerSettings = array_merge($this->providerSettings, $customSettings);
    $this->headers[] = 'Authorization: Basic '. base64_encode($this->providerSettings['ClientId'] . ':' . $this->providerSettings['ClientSecret']);
  }
 
  public function tokenRequest($code) {
    $curl = curl_init($this->providerSettings['TokenUri']);
 
    curl_setopt($curl, CURLOPT_HTTPHEADER, $this->headers);
    curl_setopt($curl, CURLOPT_POST, true);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
 
    curl_setopt($curl, CURLOPT_POSTFIELDS, http_build_query([
      'grant_type' => 'refresh_token',
      'refresh_token' => $plik,
      'redirect_uri' => $this->providerSettings['RedirectUri'],
      'api_key' => $this->providerSettings['ApiKey']
    ]));    
 
    $result = ($result = curl_exec($curl)) === false ? false : json_decode($result);
 
    if ($result === false) {
      throw new Exception('Unrecognized error');
    } else if (!empty($result->error)) {
      throw new Exception($result->error . ' - ' . $result->error_description);
    } else {
      return $result;
    }
  }
 
  public function getAuthorizationUri() {
    return $this->providerSettings['AuthorizationUri'] . '?' . http_build_query([
      'response_type' => 'code',
      'client_id' => $this->providerSettings['ClientId'],
      'api_key' => $this->providerSettings['ApiKey'],
      'redirect_uri' => $this->providerSettings['RedirectUri']
    ]);
  }
}
 
// Indywidualne parametry można podać do konstruktora w postaci tablicy, lub bezpośrednio w definicji klasy.
$auth = new AllegroOAuth2Client();
 
// Dobrze byłoby sprawdzić od kogo przychodzi żądanie
if (!empty($_GET['code'])) {
  try
  {
    $result = $auth->tokenRequest($_GET['code']);
 
 
    echo 'Twój Access Token: ' . $result->access_token . '';
    echo '<br>Twój Refresh Token: ' . $result->refresh_token . ''; 
    echo '<br>Twój expires_in:  ' . $result->expires_in . ''; 
 
file_put_contents('.verkey', $result->refresh_token);
 
 
 
  }
  catch(Exception $e)
  {
    echo $e->getMessage();
  }
} else {
  echo ' Logowanie:  <a href="'.$auth->getAuthorizationUri().'">Zaloguj do Allegro</a>';
}
 
 
?>
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