Here are two barebones examples:
1. Instant External Captive Portal with just "Accept" button: A user with "guest" as username and "guest" as password must be in the authentication server selected:
<HTML>
<form method="POST" ACTION="http(s)://securelogin.arubanetworks.com/swarm.cgi"> ## hostname must match certificate COMMON NAME
<input type="hidden" name="user" value="guest">
<input type="hidden" name="password" value="guest">
<input type="submit" name="Accept" value="authenticate">
</form>
</HTML>
2. Instant Captive Portal, username and password. User must enter username and password and click on "Login" button.
<HTML>
<form method="POST" ACTION="http(s)://securelogin.arubanetworks.com/swarm.cgi"> ## hostname must match certificate COMMON NAME
<input type="hidden" name="cmd" value="authenticate" />
User Name: <br/> <input type="text" name="user" id="user"/>
<br/>
Password: <br/> <input type="password" name="password" id="password"/>
<br/>
<input type="submit" value="Login"/>
</form>
</HTML>