ApiService::getPrinciples

public function getPrinciples($connection, $server): ?string
{
	$userId = CCalendar::GetUserId();
	$davClient = $this->createDavInstance(
		$server['scheme'],
		$server['host'],
		$server['port'],
		$connection['SERVER_USERNAME'],
		$connection['SERVER_PASSWORD']
	);
	
	$this->apiClient = new ApiClient($davClient, $userId);
	$principlesXml = $this->apiClient->propfind(
		$server['path'],
		['current-user-principal'],
		null,
		0
	);
	if ($principlesXml)
	{
		return $this->getXmlStringData(
			$principlesXml,
			'/response/propstat/prop/current-user-principal/href'
		);
	}
	
	return null;
}