$ git clone -n https://src.fedoraproject.org/rpms/R-httr.git /var/lib/mock/f40-build-1168944-21689/root/chroot_tmpdir/scmroot/R-httr
Cloning into '/var/lib/mock/f40-build-1168944-21689/root/chroot_tmpdir/scmroot/R-httr'...
$ git fetch origin f0198b5878ac2d7601ed13d2f8cb4a50167ee0a1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-httr
 * [new ref]         f0198b5878ac2d7601ed13d2f8cb4a50167ee0a1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f0198b5 R-maint-sig mass rebuild