Wed Mar 25, 2020 10:28 am
The initial login is user "ubuntu" and password "ubuntu" (you'll be prompted to change this on first login).
Alternatively, if you wish to modify these before first boot (to ensure the pi is never exposed to a network with a known user/password combination), you can customize this in the "user-data" file on the boot partition. This is part of the cloud-init configuration which performs a one-time setup on first boot. A few examples in comments are included in the file but do let me know if anything's not clear in there!
Dave.
Author of / contributor to a few pi related things (picamera, Sense HAT emulator, gpio-zero, piwheels, etc.), and currently a software engineer at Canonical responsible for Ubuntu Server and Core on the Raspberry Pi.