How set up the AD user to login the web OC auto,include first time to login.

Hi Guys!
I have configured the OC and enabled the AD users to login.
I found when I login first time,It’s need to type the AD username and password,but next time,it dosen’t need type the username and password.
So,Can I login first time without the usr and pwd?
And How to must type the usr and pwd every time?