I am having troubles when I connect with my repository through Xcode.
I have a Gitlab version (full pre-)installed on TurnkeyLinux Virtual Appliance on a remote server.
Even if the problems seems solved I've found this question when I had the problem using XCode 10. I tried logging in to GitHub and got the same error. The workaround described didn't fix my problem but I've found another solution on my own which I'd like to share – maybe it helps somebody ;)
My GitHub password included an 'ä' character (I'm German) and seems XCode and GitHub don't support the used encoding. After changing my password to something without an 'ä' it worked fine. Maybe it wasn't because of the 'ä' but it already helped to change the password - I don't know.