Login page using MVC 4 using ldap should populate domains' dropdownlist

See more:

C#

ASP.NET

C#4.0

Razor

LDAP

MVC4

I'm writing a web-app that is required to present users with a login screen.

Users can enter username/password and select a domain from a dropdown list.

how to enumerate all available domains in the server's AD forest even before user login after basic authentication? I came to know that it should be coded in Application_Start. But dont know how and what to do?

Here is my login web form which should authenticate in Active Directory

<fieldset>
        <legend>Log in Form</legend>
        <ol>
            <li>
                @Html.LabelFor(m => m.UserName)
                @Html.TextBoxFor(m => m.UserName)
                @Html.ValidationMessageFor(m => m.UserName)
            </li>
            <li>
                @Html.LabelFor(m => m.Password)
                @Html.PasswordFor(m => m.Password)
                @Html.ValidationMessageFor(m => m.Password)
            </li>
        </ol>
        <input type="submit" value="Log in" />
    </fieldset>

how to give here with a dropdown list under user name and password and should populate with list of all available domains...?

Please guide me..

Kindest Regards
Karthik