
To change the authentication first you need to login to the Administrator site.
Now select Application Management and click on the link Authentication Providers under Application Security.

After selecting the correct application click on the Default zone (Please note that here I am going to change the default zones’ authentication. If you are to change in another zone simply select the required zone).
In the Edit Authentication page select Forms as the Authentication Type then in Membership Provider Name type AD, which we are to setup later. Then click the Save button. As of the result of changing the authentication providers the Web.Config file will be changed accordingly automatically. But this is not enough we need to enter the membership provider details ther in site Web.Config file and Administrator site Web.Config files.
To do the necessary changes open both Web.Config files. Both files needed to be updated with the same information.
SharePoint Administration Site Web.Config
As the final step you have to change the site collection administrators. For this click on Site Collection Administrators under SharePoint Site Management in Application Management.
After verifying the selected application enter Primary Site Collection Administrator as AD:Administrator. If you want you can fill in Secondary Site Collection Administrator as well. After finishing click Ok.
Now go back to the site and try to login, you will see that the traditional windows login page is replaced with a simple login web page. Since this login page is too simple I did some improvements to the login page and created my own one as you can see below.
