PHP

There are a lots of http libraries available, however Timendo recommends Guzzle

Here is an example:

require 'vendor/autoload.php';
use GuzzleHttp\Client;

$username = "username";
$password = "password";
$base_url = "https://sandbox.clicrdv.com";
$path = "/api/v1/groups/:group_id/vevents.json";
$apikey = "apikey";

$client = new Client([
    'base_url' => [$base_url, []],
    'defaults' => [
        'query'   => ['apikey' => $apikey],
        'auth'    => [$username, $password],
    ]
]);

$response = $client->get($path);

### debug
echo $base_url.$path
echo $response->getBody();