In what scenarios should the choice between identifying the server or the client be considered when executing external URLs in PHP?

When executing external URLs in PHP, the choice between identifying the server or the client should be considered in scenarios where the external URL requires authentication or specific headers that are tied to either the server or the client. For example, if the external URL requires a user-specific token for authentication, it should be identified as the client. On the other hand, if the external URL requires server-specific headers or authentication, it should be identified as the server.

// Example of identifying the client when executing an external URL
$externalUrl = 'https://example.com/api/resource';
$token = 'your_user_token_here';

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $externalUrl);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Authorization: Bearer ' . $token
));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

$response = curl_exec($ch);

if($response === false){
    echo 'Error: ' . curl_error($ch);
}

curl_close($ch);