Please read the following, it is very important for your printer's health!
OctoPrint by default now ships with Access Control enabled, meaning you won't be able to do anything with the
printer unless you login first as a configured user. This is to prevent strangers - possibly with
malicious intent - to gain access to your printer via the internet or another untrustworthy network
and using it in such a way that it is damaged or worse (i.e. causes a fire).
It looks like you haven't configured access control yet. Please set up an username and password for the
initial administrator account who will have full access to both the printer and OctoPrint's settings, then click
on "Keep Access Control Enabled":
Note: In case that your OctoPrint installation is only accessible from within a trustworthy network and you don't
need Access Control for other reasons, you may alternatively disable Access Control. You should only
do this if you are absolutely certain that only people you know and trust will be able to connect to it.
Do NOT underestimate the risk of an unsecured access from the internet to your printer!