How can you send an ETag with PHP when making requests to the YouTube API?

When making requests to the YouTube API, you can send an ETag header to enable caching and reduce bandwidth usage. You can generate an ETag based on the response content and send it with subsequent requests. This allows the API to check if the content has changed since the last request, and if not, return a 304 Not Modified response. 

// Generate ETag based on response content
$etag = md5($response_content);

// Send ETag with subsequent requests
$options = [
    'http' => [
        'header' => "ETag: $etag"
    ]
];

$context = stream_context_create($options);
$response = file_get_contents('https://www.googleapis.com/youtube/v3/videos', false, $context);

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