If you have EP/Role Centers rolled out in your intranet with Kerberos configured ( refer to Kerberos configuration document )  and now would like to expose this to your domain users outside of your corpnet, for example employee would access their role center from home, then you need to additionally configure Kerberos protocol configuration. You might have got enabled your firewall settings to allow them to access the EP and Reporting servers from outside network. Since the user comes outside of the network, IE will prompt them to enter the user account / password even though IIS authentication is set to windows integrated authentication. In this case, for Kerberos to work you need to configure protocol transition in Kerberos. To do that
1. Open up your “Active Directory Users and Computers” admin tool on your domain controller and locate the user account that you are using as business connector proxy and right click and open up its properties window.
2. Navigate to the “Delegation” tab and change the setting to “Trust this user for delegation to specified services only” and “User any authenticate protocol”.
3. Click the add button in the “Delegation” tab. It will bring up the “Add Services” dialog.
4. Click on the “Users or Computers” button. It will bring up the “Select Users or Computers” dialog.
5. Enter the account that is used as business proxy account ( This is the same account that the EP and report web site use as the application pool and the SSAS window service logon account).
6. Click “OK”. This will close the “Select Users or Computers” dialog and list the services (SPNs registered for Kerberos for the bc proxy account) in the “All Services” list of “Add Services: dialog.
7. Click “Select All” and then “OK” in “Add Services” dialog. This will close “ADD Services dialog” and list them in “Services to which this account can present delegated credentials” list in the “Delegation” tab.
8. Click “OK” to save this setting to the user account.
9. Do “IISReset” on the EP server



The alternate approach could be to use ISA 2006 as the firewall and let ISA collect the user account/password using a form over ssl and ISA will user Kerberos constrained delegation.
http://technet.microsoft.com/en-us/library/bb794858.aspx