I'm guessing that mod_auth_gssapi is not actually *needed* by the Koji code base, it's just the recommended way to configure Kerberos authentication for the web UI, right? But in my installation I am just using SSL certs anyway.

So the easiest solution would be to just drop this Requires on EL6.

In upstream, we have the following:
%if 0%{?fedora} >= 21 || 0%{?rhel} >= 7
Requires: mod_auth_gssapi
%else
Requires: mod_auth_kerb
%endif

(and similar for the hub)

Fedora carries their own spec changes.

Can you try this scratch build: 

https://koji.fedoraproject.org/koji/taskinfo?taskID=43780000

FEDORA-EPEL-2020-f2d964c080 has been submitted as an update to Fedora EPEL 6. https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2020-f2d964c080

FEDORA-EPEL-2020-e9d34610c0 has been submitted as an update to Fedora EPEL 7. https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2020-e9d34610c0

FEDORA-2020-69cb41f2c7 has been submitted as an update to Fedora 32. https://bodhi.fedoraproject.org/updates/FEDORA-2020-69cb41f2c7

FEDORA-2020-5088f068f4 has been submitted as an update to Fedora 30. https://bodhi.fedoraproject.org/updates/FEDORA-2020-5088f068f4

FEDORA-2020-edd79688a9 has been submitted as an update to Fedora 31. https://bodhi.fedoraproject.org/updates/FEDORA-2020-edd79688a9

FEDORA-2020-edd79688a9 has been pushed to the Fedora 31 testing repository.
In short time you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --advisory=FEDORA-2020-edd79688a9`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2020-edd79688a9

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

FEDORA-EPEL-2020-e9d34610c0 has been pushed to the Fedora EPEL 7 testing repository.

You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2020-e9d34610c0

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

FEDORA-EPEL-2020-f2d964c080 has been pushed to the Fedora EPEL 6 testing repository.

You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2020-f2d964c080

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

FEDORA-2020-5088f068f4 has been pushed to the Fedora 30 testing repository.
In short time you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --advisory=FEDORA-2020-5088f068f4`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2020-5088f068f4

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

FEDORA-2020-69cb41f2c7 has been pushed to the Fedora 32 testing repository.
In short time you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --advisory=FEDORA-2020-69cb41f2c7`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2020-69cb41f2c7

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

FEDORA-2020-69cb41f2c7 has been pushed to the Fedora 32 stable repository.
If problem still persists, please make note of it in this bug report.

FEDORA-EPEL-2020-f2d964c080 has been pushed to the Fedora EPEL 6 stable repository.
If problem still persists, please make note of it in this bug report.

FEDORA-EPEL-2020-e9d34610c0 has been pushed to the Fedora EPEL 7 stable repository.
If problem still persists, please make note of it in this bug report.

FEDORA-2020-edd79688a9 has been pushed to the Fedora 31 stable repository.
If problem still persists, please make note of it in this bug report.

FEDORA-2020-5088f068f4 has been pushed to the Fedora 30 stable repository.
If problem still persists, please make note of it in this bug report.