API license key plugin form. Visit blog post https://bit.ly/2xlZKGx

api_license_key_plugin_form.php

<h1>License Key</h1>

<?php if ($error_message):?>
  <div class="notice notice-error is-dismissible"> 
    <p><strong><?php echo $error_message;?></strong></p>
    <button type="button" class="notice-dismiss">
      <span class="screen-reader-text">Dismiss this notice.</span>
    </button>
  </div>
<?php endif; ?>
<?php if ($success_message):?>
  <div class="notice notice-success is-dismissible"> 
    <p><strong><?php echo $success_message;?></strong></p>
    <button type="button" class="notice-dismiss">
      <span class="screen-reader-text">Dismiss this notice.</span>
    </button>
  </div>
<?php endif; ?>

<form action="?page=plugin-name&action=auth" method="post">
  <input type="text" id="user" name="user" value="" required />
  <input type="password" id="password" name="password" value="" required />
  <input type="submit" value="Login" class="button button-primary" />
</form>

<?php if ($logged_in === true) :?>
  <?php if (get_option('license_key_is_confirmed')):?>
    <form action="?page=plugin-name&action=deactivate" method="post">
      <input type="hidden" name="user" value="<?php echo $_POST['user'];?>" />
      <input type="hidden" name="password" value="<?php echo $_POST['password'];?>" />
      <input type="text" id="pro-licence" name="pro-licence" value="<?php echo $license_key;?>" readonly />
      <input type="submit" value="Deactivate License" class="button button-primary" />
    </form>
  <?php else:?>
    <form action="?page=ctrls&action=activate" method="post">
      <input type="hidden" name="user" value="<?php echo $_POST['user'];?>" />
      <input type="hidden" name="password" value="<?php echo $_POST['password'];?>" />
      <input type="text" id="pro-licence" name="pro-licence" value="<?php echo $license_key;?>" readonly />
      <input type="submit" value="Activate License" class="button button-primary" />
    </form>
  <?php endif;?>
<?php endif;?>