Throw Exception if OAuth is attempted (#42)

Temporary update to throw an exception if OAuth is attempted due to OOB deprecation: https://developers.googleblog.com/2022/02/making-oauth-flows-safer.html#disallowed-oob

A new, approved OAuth flow will be added in the future.

removed the getToken method and lines 317-324 so we don't demonstrate an unsupported approach + we avoid unreachable code.

php/ContentSession.php

@@ -299,29 +299,8 @@ public function getHome() {
     return rtrim($home, '\\/');
   }
 
-  private function getToken(Google_Client $client) {
-    $client->setRedirectUri('urn:ietf:wg:oauth:2.0:oob');
-    $client->setScopes('https://www.googleapis.com/auth/content');
-    $client->setAccessType('offline'); // So that we get a refresh token
-
-    printf("Visit the following URL and log in:\n\n\t%s\n\n",
-        $client->createAuthUrl());
-    print ('Then type the resulting code here: ');
-    $code = trim(fgets(STDIN));
-    $client->authenticate($code);
-
-    return $client->getAccessToken();
-  }
-
   protected function cacheToken(Google_Client $client) {
-    print (str_repeat('*', 40) . "\n");
-    print ("Your token was missing or invalid, fetching a new one\n");
-    $token = $this->getToken($client);
-    $tokenFile = join(DIRECTORY_SEPARATOR,
-        [$this->configDir, self::OAUTH_TOKEN_FILE_NAME]);
-    file_put_contents($tokenFile, json_encode($token, JSON_PRETTY_PRINT));
-    printf("Token saved to %s\n", $tokenFile);
-    print (str_repeat('*', 40) . "\n");
+    throw new Exception('This example currently only supports the service account flow..');
   }
 
   /**