F5 LTM doesnt pass the credential to server.

You need to capture the traffic using an HTTP debug tool, like HttpWatch or Fiddler, and collect the traffic via F5 and direct to the server. It will tell you what is different, and where to look next. Probably, it will show you that the authentication is sent to a different URL.

If you need help to understand the output, post here (also the relevant part of the F5 configuration), and I will have a look.