Boom, fixed it! I’m showing the HA page on a RPi with Raspbian Lite, (HA itselfs runs on a different system).
I’m running a command which moves the mouse and clicks the button!
Running this command (for 1920x1080 screens):
export XAUTHORITY=/home/USERNAME/.Xauthority; export DISPLAY=:0; xdotool mousemove 960 463; xdotool sleep 2; xdotool click 1
Run this command e.g. 3 minutes after booting, and you’ll be logged in automaticcaly! You can even use this command to ‘click’ the ‘Save Login’ in the lower right corner (anoying on kiosk browsers).
Works like a charm!!!
EDIT 7 APRIL 2021:
Looks like the button has moved now. Please change the mouse coordinates to: 960 410
thus:
export XAUTHORITY=/home/USERNAME/.Xauthority; export DISPLAY=:0; xdotool mousemove 960 410; xdotool sleep 2; xdotool click 1