If you are trying to access the portal from the webserver you might get a login prompt. This can be due to the loopback check being on. You can disable it with the following registry key.
1 - open regedit
2 - go to
3 - Add DWORD KEY : disableloopbackcheck
right-click in the white area -new - DWORD (32-Bit) Value
Change New Value #1 to disableloopbackcheck
Change Value to : 1