change.php

<?php
if (isset($_POST['login'])
    && isset($_POST['old_pswd'])
        && isset($_POST['change_pswd'])
            && isset($_POST['change_pswd_sec']))
    {

        $login = $_POST['login'];
        $login = stripslashes($login);
        $login = trim($login);
        $login = htmlspecialchars($login);

        $password = $_POST['old_pswd'];
        $password = stripslashes($password);
        $password = trim($password);
        $password = htmlspecialchars($password);

        $password_new = $_POST['change_pswd'];
        $password_new = stripslashes($password_new);
        $password_new = trim($password_new);
        $password_new = htmlspecialchars($password_new);

        $password_new_sec = $_POST['change_pswd_sec'];
        $password_new_sec = stripslashes($password_new_sec);
        $password_new_sec = trim($password_new_sec);
        $password_new_sec = htmlspecialchars($password_new_sec);

        if(empty($password_new))
        {
            echo 'Error: Password not specified!';
            echo "<script>setTimeout('location=document.location.href', 8000 )</script>";
        }

        if ($password_new == $password_new_sec) {

            include 'a_api.php';

            $result = $proxy->checkPassword($login, $password);

            if (!$result->isOk()) {
                echo 'Error: Incorrect old account password!';
                echo "<script>setTimeout('location=document.location.href', 8000 )</script>";

            }else{
                $result = $proxy->changePassword($login, $password_new);
                if ($result->isOk()) {
                    echo 'Password changed!';
                    echo "<script>setTimeout('location=document.location.href', 8000 )</script>";
                }else{
                    echo 'Error: ' . $result->toString();
                    echo "<script>setTimeout('location=document.location.href', 8000 )</script>";
                    }
                }

            } else {
                echo 'Error: Password mismatch!';
                echo "<script>setTimeout('location=document.location.href', 8000 )</script>";
            }
    } else { ?>


<form method="post" style="max-width:500px;margin:auto">
<h2>Change password</h2>

<div class="input-container">
    <i class="fa fa-user icon"></i>
    <input placeholder="Username" class="input-field" type="text" name="name" pattern="[A-Za-z0-9]{4,16}" required />
  </div>


  <div class="input-container">
    <i class="fa fa-key icon"></i>
    <input placeholder="Old Password" class="input-field" autocomplete="new-password" type="password" name="old_pswd" pattern="[A-Za-z0-9]{4,16}" required />
  </div>

  <div class="input-container">
    <i class="fa fa-key icon"></i>
    <input placeholder="New Password" class="input-field" autocomplete="new-password" type="password" name="change_pswd" pattern="[A-Za-z0-9]{4,16}" required />
  </div>

  <div class="input-container">
    <i class="fa fa-key icon"></i>
    <input placeholder="Repeat Password" class="input-field" autocomplete="new-password" type="password" name="change_pswd_sec" pattern="[A-Za-z0-9]{4,16}" required />
  </div>

  <div class="input-container">
  <button type="submit" class="btn" name="pswd_submit" value="Chanege Password!"> Chanege Password!</button>
  </div>

  <p><a href="?">Back to Register Form!</a></p>
</form>

<?php }
?>