public function getAuthorizationUrl($redirectUri = null, $state = null, array $params = [])
    {
        //Request Parameters
        $params = array_merge([
            'client_id' => $this->getApp()->getClientId(),
            'response_type' => 'code',
            'state' => $state,
            ], $params);

        if (!is_null($redirectUri)) {
            $params['redirect_uri'] = $redirectUri;
        }

        return $this->buildUrl('/oauth2/authorize', $params);
    }