Save Inno Setup custom page field values to an INI file

How do I read and store the values of two page field values to an INI file? I created two key pairs at the INI section using ISTool. Now how do I link this up?

The INI Section looks like this:

[INI]
Filename: {app}\prefs.ini; Section: AUTH; Key: USERNAME; String: 
Filename: {app}\prefs.ini; Section: AUTH; Key: PASSWORD; String: 

Page is created like this:

AuthPage := CreateInputQueryPage(wpWelcome,
  'Account Information', 'Please enter your Account Information',
  '');
AuthPage.Add('Username:', False);
AuthPage.Add('Password:', True);

EDIT:

I made the following additions. It doesn't work for some reason:

SetIniString('AUTH', 'USERNAME', AuthPage.Values[0], '{app}\prefs.ini')
SetIniString('AUTH', 'PASSWORD', AuthPage.Values[1], '{app}\prefs.ini')