You can use the next=otherurl query parameter to the login page. That’ll redirect jupyter after you login. We do something similar to step into a specific directory.
If this is an entirely separate jupyter app then you can just hard code the .ipynb file there.
If it’s for say you’re production app where you want to give folks a checkbox toggle to do this, open to a specific file, OR just open to your home it’d be a little more complicated, but it’s basically the same scheme we do with jupyter_api. We have a checkbox to work in a class room environment and if it’s checked, we set the jupyter_api environment variable in the before.sh.erb and pass it back to the UI through conn_params in the submit.yml.erb.