Yii team relased official HTTP client extension created mainly by Paul Klimov. The extension itself was ready for release long time ago but since there's PSR-7, there were debates about should it be released without it. Finally, it was decided that it's a good idea since, first of all, it's already adopted by many projects, and second, PSR-7 support could be added in further major versions.

Composing and performing HTTP requests looks like the following:

use yii\httpclient\Client;

$client = new Client();
$response = $client->createRequest()
    ->setMethod('post')
    ->setUrl('http://example.com/api/1.0/users')
    ->setData(['name' => 'John Doe', 'email' => 'johndoe@domain.com'])
    ->send();
if ($response->isOk) {
    $newUserId = $response->data['id'];
}