I've been using HTTPS but never have to type in my credentials.
That is probably because your credentials are already cached by a credential helper.
- Check what yours is: git config --global credential.helper
- Check what credentials are stored:
In a Git bash session:
printf "host=github.com\nprotocol=https" | git-credential-xxx get
Replace xxx by the value returned by git config --global credential.helper.
If it is empty, and if the remote URL is an HTTPS one, then, as suggested by LeGEC in the comments, Git might still be using SSH anyway with an url.<base>.pushInsteadOf directive.
Check that with:
git config --show-origin --list --show-scope | grep -i insteadOf
The OP adds in the comments:
running git config --show-origin --list gives me, among other things, file:/Applications/Xcode.app/Contents/Developer/usr/share/git-core/gitconfig    credential.helper=osxkeychain
So it could look like it is stored in my osxkeychain?
If that is the case:
printf "host=github.com\nprotocol=https" | git-credential-osxkeychain get
See also "Updating credentials from the macOS Keychain".