public function authenticationUrl($redirect, $approvalPrompt = 'auto', $scope = null, $state = null)
{
$parameters = array('client_id' => $this->clientId, 'redirect_uri' => $redirect, 'response_type' => 'code', 'approval_prompt' => $approvalPrompt, 'state' => $state);
if (!is_null($scope)) {
$parameters['scope'] = $scope;
}
return $this->parseGet($this->authUrl . 'authorize', $parameters);
}