How to change the default RDWeb login page domain
This can be changed to make it easier for users to login with the correct domain, simply edit the file C:\Windows\Web\RDWeb\Pages\en-US\login.aspx with your default domain name.
The line you need to edit is line 386, just swap out YOURDOMAIN with the domain name for your site
<label><input id="DomainUserName" name="DomainUserName" type="text" class="textInputField" runat="server" size="25" autocomplete="off" value="YOURDOMAIN\" /></label>