Hi,
I'm not sure if the OP is still looking for a solution for streaming to DaCast, but I was able to find some help through this post
https://jp9000.github.io/OBS/general/auth.html.
My solution is a little different from the one suggested in the post, I'll outline what I did and hope it points other people in the correct direction for their own situations. I'm using the 64bit multi-platform version on win7.
I created a new profile within OBS called Dacast, you can duplicate one of your existing profiles if you want. I then found the basic.ini file within my DaCast profile folder, on my system it was located in C:\Users%Appdata%\Roaming\obs-studio\basic\profiles\Dacast
Open the basic.ini file and add the following entry at the end of the file:
[Publish]
UserName= <enter_user_name_here>
Password= <enter_user_password_here>
*Replace the enter username and password with the real values received from DaCast
After this, restart OBS and hit the start streaming.
Hope this helps someone out there.