I just set up an EMR cluster with built-in Spark, JupyterHub and so on. I am able to access the Jupyter Notebook at http://master_hostname:9443/hub/login but I have no idea what credential I can use to log in or where I can set this up in the EMR.
As documented here https://docs.aws.amazon.com/emr/latest/ReleaseGuide/emr-jupyterhub-user-access.html
the default admin is named "jovyan" and the password is "jupyter" :)