将代码点火器表单验证与 Web 服务结合使用

我想知道，如何将Codeigniter的表单验证与Web服务一起使用？我正在使用 REST 和 cURL 与 Web 服务连接，并尝试在登录页面上使用表单验证。当用户名或密码字段为空时，我可以让它返回错误，但不确定如何使用它来检查密码是否匹配。我的 cUrl 代码如下：

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_HEADER, false);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("X-DocuSign-Authentication: $header"));
curl_setopt($ch, CURLOPT_UNRESTRICTED_AUTH, 1);
$output = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
$this->form_validation->set_rules('username', 'USERNAME', 'required|is_unique[username]');
$this->form_validation->set_rules('password', 'PASSWORD', 'required|matches[password]');
if ($this->form_validation->run() == FALSE) {
    curl_close($ch);
    $this->load->view('error_login');
} else {        
    $response = json_decode($output, true);
    $accountId = $response["loginAccounts"][0]["accountId"];
    $baseUrl = $response["loginAccounts"][0]["baseUrl"];
    $userName = $response["loginAccounts"][0]["userName"];
    curl_close($ch);
    $username = $userName;
    $docusignURL = $baseUrl;
    $docHeader = $header;
    $loggedIn = array('is_logged_in' => true);
    $this->session->set_userdata('username', $username);
    $this->session->set_userdata('docusignURL', $docusignURL);
    $this->session->set_userdata('docHeader', $docHeader);
    $this->session->set_userdata($loggedIn);
    redirect('/create_envelope', 'refresh');
}

现在它返回两个错误通知，"未定义的偏移量：1"和"未定义的属性：登录：：$db"。后者是因为，我假设，我没有使用模型连接到任何数据库。任何有用的建议都将非常出色。

编辑：所以我尝试了回调路由，但我收到500错误。这是我到目前为止的整个控制器代码：

<?php
    class Login extends CI_Controller {
        function index() {
            $this->load->view('al_login');
        }
        function authenticate(){
            $post = $this->input->post();
            extract($post);
            $integratorKey = '****-********-****-****-****-************';       
            $header = "<DocuSignCredentials><Username>" . $username . "</Username><Password>" . $password . "</Password><IntegratorKey>" . $integratorKey . "</IntegratorKey></DocuSignCredentials>";
            $url = "https://demo.docusign.net/restapi/v2/login_information";
            $ch = curl_init();
            curl_setopt($ch, CURLOPT_URL, $url);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
            curl_setopt($ch, CURLOPT_HEADER, false);
            curl_setopt($ch, CURLOPT_HTTPHEADER, array("X-DocuSign-Authentication: $header"));
            curl_setopt($ch, CURLOPT_UNRESTRICTED_AUTH, 1);
            $output = curl_exec($ch);
            $status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
            $response = json_decode($output, true);
            $accountId = $response["loginAccounts"][0]["accountId"];
            $baseUrl = $response["loginAccounts"][0]["baseUrl"];
            $userName = $response["loginAccounts"][0]["userName"];
            curl_close($ch);
            $username = $userName;
            $docusignURL = $baseUrl;
            $docHeader = $header;
            $loggedIn = array('is_logged_in' => true);
            $this->session->set_userdata('username', $username);
            $this->session->set_userdata('docusignURL', $docusignURL);
            $this->session->set_userdata('docHeader', $docHeader);
            $this->session->set_userdata($loggedIn);
            $this->form_validation->set_rules('username', 'USERNAME', 'required');
            $this->form_validation->set_rules('password', 'PASSWORD', 'required|callback_password_check');
            if ($this->form_validation->run() == FALSE) {
                $this->load->view('al_login');
            } else {
                $this->load->view('/create_envelope');
            }
        }
        function password_check($str){
            // send the user name to the service 
            if ( $this->authenticate($str) == true ) {
                return true; 
            } else { 
                // customize the message with something 
                $this->form_validation->set_message('password_check', 'The %s is incorrect. Please try again');
                return false;
            } 
        }       
    }

我是REST，cURL和Codeigniter的新手，所以我的知识可以提供帮助。到目前为止，感谢你们俩。知道为什么我会收到 500 个错误吗？

新编辑： @Petre 因此，这是我们网络服务的响应：

Array ( 
    [loginAccounts] => Array ( 
        [0] => Array ( 
            [name] => ******** 
            [accountId] => ******* 
            [baseUrl] => https://demo.docusign.net/restapi/v2/accounts/******* 
            [isDefault] => true 
            [userName] => **** ******** 
            [userId] => ********-****-****-****-************ 
            [email] => ****@******.com
            [siteDescription] => 
        ) 
    ) 
)

似乎不是那种东西。