0 if this callback has created the commit and populated the out parameter, GIT_PASSTHROUGH if the callback has not created a commit and wants the calling function to create the commit as if no callback had been specified, any other value to stop and return a failure
Commit creation callback: used when a function is going to create commits (for example, in git_rebase_commit) to allow callers to override the commit creation behavior. For example, users may wish to sign commits by providing this information to git_commit_create_buffer, signing that buffer, then calling git_commit_create_with_signature. The resultant commit id should be set in the out object id parameter.