Issue
Edit
Basic protocol now found from some notes. But Seir has already answered so I probably can't delete this. Her/his answer may be useful to someone though.
I use GitLab, not Github. This question is specific to the former.
I push to and pull from projects using both W10 and Linux (Mint 20).
I really know next to nothing about communicating with the GitLab server, or what SSH keys are and how they work (I have read about them but still don't understand). I've found virtually no documentation at GitLab explaining what I should be doing.
In W10: I can push without ever being asked for username + password. This applies even when I have just created a new project. It is lost in the mists of time how I set this up... and I don't know how to find out. I have a suspicion this might be "HTTPS" access.
In Linux: when I push I always have to enter username + password. I don't know whether things can be set up so I never have to enter username + password, or whether I have to do this on a per-project basis. One of my projects never asks for username + password. The last time I tried setting things up was about 2 years ago. Maybe I succeeded with this one project.
Can someone explain what I have to do or point me to a source of information for my very low level of understanding?
Solution
You have to setup an SSH key for each individual system. I suspect you've already added an SSH key for your W10 system.
Navigate to your user settings → SSH Keys
Now click on the link 'generate one' and follow the instructions.
GitLab Docs: Use SSH keys to communicate with GitLab
Answered By - Seir Answer Checked By - David Marino (WPSolving Volunteer)