about AUTHENTICATION mode plain

[horsley]

I want to ask why ocserv using plain authentication response the auth xml in two 
step?

first is Please enter your username

<?xml version="1.0" encoding="UTF-8"?>
<config-auth client="vpn" type="auth-request">
<version who="sg">0.1(1)</version>
<auth id="main">
<message>Please enter your username</message>
<form method="post" action="/auth">
<input type="text" name="username" label="Username:" />
</form></auth>
</config-auth>

and then the password

That's make the client prompt twice, and while I use an url to control 
the client externally like 
anyconnect:connect?name=vpn&host=abc.com
&prefill_username=user&prefill_password=pass

it's still prompt for password.(username is prefill ok but password are not)

so why not send the complete auth request including user and password in 
the xml form together?