Why does reposync fails with "[Received HTTP code 407 from proxy after CONNECT]" ?

Issue

• Reposync fails with the error on system behind proxy.

# reposync -p <download-path> --download-metadata --repo=<repo id>
.
.
[FAILED] insights-client-3.1.7-7.el8_6.noarch.rpm: No more mirrors to try - All mirrors were already tried without success
[MIRROR] perl-Text-Diff-1.44-3.module+el8+2464+d274aed1.noarch.rpm: Curl error (56): Failure when receiving data from the peer for https://cdn.redhat.com/content/dist/rhel8/8/x86_64/appstream/os/Packages/p/perl-Text-Diff-1.44-3.module%2bel8%2b2464%2bd274aed1.noarch.rpm [Received HTTP code 407 from proxy after CONNECT]
[MIRROR] bpg-sans-regular-fonts-1.005-10.el8.noarch.rpm: Curl error (56): Failure when receiving data from the peer for https://cdn.redhat.com/content/dist/rhel8/8/x86_64/appstream/os/Packages/b/bpg-sans-regular-fonts-1.005-10.el8.noarch.rpm [Received HTTP code 407 from proxy after CONNECT]
[FAILED] bpg-sans-regular-fonts-1.005-10.el8.noarch.rpm: No more mirrors to try - All mirrors were already tried without success
[FAILED] perl-Text-Diff-1.44-3.module+el8+2464+d274aed1.noarch.rpm: No more mirrors to try - All mirrors were already tried without success