Hello there, I had the same issue with my Kobo and found that in order to get the username and password across you had to put it into the URL like this:
https://user:Password@IPaddress/mobile
Not sure if you use SSL so you may not need the https bit. As an example if your details were:
user: cootey
password: Password1
server address: 192.168.0.125
the URL you would put into the kobo browser would be:
https://cootey:Pa$$word1@192.168.0.125/mobile
Hope this helps
Dom