Google API login failed always: back to needing to authorize - oauth-2.0

Question

I'd like to change my tags of a YouTube video using the YouTube Data API. But I'm already stuck on login:
My page shows the message: You need to authorize access before proceeding. I click on authorize access and select my Google account and then my YouTube channel, I select allow and get redirected to the login message.
The code is directly from the sample files on Github:
<?php
/**
* This sample adds new tags to a YouTube video by:
*
* 1. Retrieving the video resource by calling the "youtube.videos.list" method
* and setting the "id" parameter
* 2. Appending new tags to the video resource's snippet.tags[] list
* 3. Updating the video resource by calling the youtube.videos.update method.
*
* #author Ibrahim Ulukaya
*/
/**
* Library Requirements
*
* 1. Install composer (https://getcomposer.org)
* 2. On the command line, change to this directory (api-samples/php)
* 3. Require the google/apiclient library
* $ composer require google/apiclient:~2.0
*/
if (!file_exists(__DIR__ . '/vendor/autoload.php')) {
throw new \Exception('please run "composer require google/apiclient:~2.0" in "' . __DIR__ .'"');
}
require_once __DIR__ . '/vendor/autoload.php';
session_start();
/*
* You can acquire an OAuth 2.0 client ID and client secret from the
* {{ Google Cloud Console }} <{{ https://cloud.google.com/console }}>
* For more information about using OAuth 2.0 to access Google APIs, please see:
* <https://developers.google.com/youtube/v3/guides/authentication>
* Please ensure that you have enabled the YouTube Data API for your project.
*/
$OAUTH2_CLIENT_ID = 'myID';
$OAUTH2_CLIENT_SECRET = 'mySec';
$client = new Google_Client();
$client->setClientId($OAUTH2_CLIENT_ID);
$client->setClientSecret($OAUTH2_CLIENT_SECRET);
$client->setScopes('https://www.googleapis.com/auth/youtube');
$redirect = filter_var('http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'],
FILTER_SANITIZE_URL);
$client->setRedirectUri($redirect);
// Define an object that will be used to make all API requests.
$youtube = new Google_Service_YouTube($client);
// Check if an auth token exists for the required scopes
$tokenSessionKey = 'token-' . $client->prepareScopes();
if (isset($_GET['code'])) {
if (strval($_SESSION['state']) !== strval($_GET['state'])) {
die('The session state did not match.');
}
$client->authenticate($_GET['code']);
$_SESSION[$tokenSessionKey] = $client->getAccessToken();
header('Location: ' . $redirect);
}
if (isset($_SESSION[$tokenSessionKey])) {
$client->setAccessToken($_SESSION[$tokenSessionKey]);
}
// Check to ensure that the access token was successfully acquired.
if ($client->getAccessToken()) {
$htmlBody = '';
try{
// REPLACE this value with the video ID of the video being updated.
$videoId = "Zqt-NvuMKYU";
// Call the API's videos.list method to retrieve the video resource.
$listResponse = $youtube->videos->listVideos("snippet",
array('id' => $videoId));
// If $listResponse is empty, the specified video was not found.
if (empty($listResponse)) {
$htmlBody .= sprintf('<h3>Can\'t find a video with video id: %s</h3>', $videoId);
} else {
// Since the request specified a video ID, the response only
// contains one video resource.
$video = $listResponse[0];
$videoSnippet = $video['snippet'];
$tags = $videoSnippet['tags'];
// Preserve any tags already associated with the video. If the video does
// not have any tags, create a new list. Replace the values "tag1" and
// "tag2" with the new tags you want to associate with the video.
if (is_null($tags)) {
$tags = array("tag1", "tag2");
} else {
array_push($tags, "tag1", "tag2");
}
// Set the tags array for the video snippet
$videoSnippet['tags'] = $tags;
// Update the video resource by calling the videos.update() method.
$updateResponse = $youtube->videos->update("snippet", $video);
$responseTags = $updateResponse['snippet']['tags'];
$htmlBody .= "<h3>Video Updated</h3><ul>";
$htmlBody .= sprintf('<li>Tags "%s" and "%s" added for video %s (%s) </li>',
array_pop($responseTags), array_pop($responseTags),
$videoId, $video['snippet']['title']);
$htmlBody .= '</ul>';
}
} catch (Google_Service_Exception $e) {
$htmlBody .= sprintf('<p>A service error occurred: <code>%s</code></p>',
htmlspecialchars($e->getMessage()));
} catch (Google_Exception $e) {
$htmlBody .= sprintf('<p>An client error occurred: <code>%s</code></p>',
htmlspecialchars($e->getMessage()));
}
$_SESSION[$tokenSessionKey] = $client->getAccessToken();
} elseif ($OAUTH2_CLIENT_ID == 'REPLACE_ME') {
$htmlBody = <<<END
<h3>Client Credentials Required</h3>
<p>
You need to set <code>\$OAUTH2_CLIENT_ID</code> and
<code>\$OAUTH2_CLIENT_ID</code> before proceeding.
<p>
END;
} else {
// If the user hasn't authorized the app, initiate the OAuth flow
$state = mt_rand();
$client->setState($state);
$_SESSION['state'] = $state;
$authUrl = $client->createAuthUrl();
$htmlBody = <<<END
<h3>Authorization Required</h3>
<p>You need to authorize access before proceeding.<p>
END;
}
?>
<!doctype html>
<html>
<head>
<title>Video Updated</title>
</head>
<body>
<?=$htmlBody?>
</body>
</html>
Would be great if someone has a tip for me.

Answer 1

Fixed... was a space key inside secret