/**
  * Ensures an exception is thrown if response is missing a X-Server-Authorization-HMAC-SHA256 header.
  *
  * @expectedException \Acquia\Hmac\Exception\MalformedResponseException
  * @expectedExceptionMessage Response is missing required X-Server-Authorization-HMAC-SHA256 header.
  */
 public function testMissingServerAuthorizationHeader()
 {
     $request = new Request('GET', 'http://example.com');
     $response = new Response();
     $authenticator = new ResponseAuthenticator($request, $this->authKey);
     try {
         $authenticator->isAuthentic($response);
     } catch (MalformedResponseException $e) {
         $this->assertSame($response, $e->getResponse());
         throw $e;
     }
 }
 /**
  * Called when the middleware is handled.
  *
  * @param callable $handler
  *
  * @return \Closure
  */
 public function __invoke(callable $handler)
 {
     return function ($request, array $options) use($handler) {
         $request = $this->signRequest($request);
         $promise = function (ResponseInterface $response) use($request) {
             $authenticator = new ResponseAuthenticator($request, $this->key);
             if (!$authenticator->isAuthentic($response)) {
                 throw new MalformedResponseException('Could not verify the authenticity of the response.', null, 0, $response);
             }
             return $response;
         };
         return $handler($request, $options)->then($promise);
     };
 }