$ git clone -n https://src.fedoraproject.org/rpms/R-httr.git /var/lib/mock/f42-build-side-1-3500327-45970/root/chroot_tmpdir/scmroot/R-httr
Cloning into '/var/lib/mock/f42-build-side-1-3500327-45970/root/chroot_tmpdir/scmroot/R-httr'...
$ git fetch origin 255c1b30ad3b9861b5d1aa343257bc7c839e3994:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-httr
 * [new ref]         255c1b30ad3b9861b5d1aa343257bc7c839e3994 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 255c1b3 R-maint-sig mass rebuild