How do convert PHP curl in ASP.NET (httpwebrequest )

I want to convert this php curl into asp.net . I am a beginner in asp.net , can someone here help me to convert this curl into asp.net. please . 

$handle = curl_init();
if ($this->accessToken) {
            // Access token is used in OAuth2 flow
            $url .= '?access_token=' . $this->accessToken;
        } else if ($this->token) {
            // Auth token is taken from PG account
            $url .= '?auth_token=' . $this->token;
        } else {
            // if using username and password - pass them as curl option
            curl_setopt($handle, CURLOPT_USERPWD, $this->username . ':' . $this->password);
        }
        curl_setopt($handle, CURLOPT_URL, $url);
        curl_setopt($handle, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($handle, CURLOPT_CUSTOMREQUEST, strtoupper($method));
        curl_setopt($handle, CURLOPT_HTTPHEADER, array(
            'Content-type: multipart/form-data;',
        ));

        // if request has additional options - add them to request
        if (! empty($options)) {

            // extract files, pass them separately
            $files = array();
            foreach ($options as $key => $value) {
                if (! empty($value) && ! is_array($value) && $value[0] === '@') {
                    $files[$key] = $this->toCurlFile($value);
                    unset($options[$key]);
                }
            }
  $data = $files;
            if (! empty($options)) {
                // original API requires data to be in json format
                $data = array_merge($data, array(
                    'data' => json_encode($options),
                ));
            }
            curl_setopt($handle, CURLOPT_POSTFIELDS, $data);
        }
        $response = curl_exec($handle);

I have tried to convert this using httpwebrequest in asp.net . but given below line of php confusing me. that is the reason , I am not able to  start this work to convert it in asp.net. 
curl_setopt($handle, CURLOPT_URL, $url);
        curl_setopt($handle, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($handle, CURLOPT_CUSTOMREQUEST, strtoupper($method));
        curl_setopt($handle, CURLOPT_HTTPHEADER, array(
            'Content-type: multipart/form-data;',