$ git clone -n https://src.fedoraproject.org/rpms/rust-base64_0.13.git /var/lib/mock/f38-build-side-43-rust-devel-1411452-31436/root/chroot_tmpdir/scmroot/rust-base64_0.13
Cloning into '/var/lib/mock/f38-build-side-43-rust-devel-1411452-31436/root/chroot_tmpdir/scmroot/rust-base64_0.13'...
$ git fetch origin cb12bc595c003e392b58c793a72adc2267d360c3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-base64_0.13
 * [new ref]         cb12bc595c003e392b58c793a72adc2267d360c3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cb12bc5 Initial import (base64 0.13 compat package)