Add `Signed-off-by` in commit messages for bots

I suppose that the responsibility for adding Signed-off-by into commit messages is on the GitHub application side. Is that correct?
So whenever some GitHub bot (dependabot, Snyk, …) creates new commit, the bot itself have to add Signed-off-by in commit message? And the bot provider/producer/author should (in best case) provide interface to setup this? Does it have to be implemented on the bot side?

Or is there any other process or procedure to be done/to setup on the GitHub environment to add Signed-off-by into commit messages automatically by bots?