I know how to sign standard commits using magit, but I'm not able to sign the commits generated by merges. Is there any way to do that?
You can add additional options to an existing popup:
(magit-define-popup-option 'magit-merge-popup
?S "Sign using gpg" "--gpg-sign=" magit-read-gpg-secret-key)
This was copied straight from magit-commit-popup
.
Also see https://github.com/magit/magit/wiki/Additional-proposed-infix-arguments-and-suffix-commands.