It was discovered that the python-requests Proxy-Authorization header was never re-evaluated when a redirect occurs. The Proxy-Authorization header was sent to any new proxy or non-proxy destination as redirected.
Created python-requests tracking bugs for this issue:
Affects: fedora-all [bug 1046627]
Affects: epel-7 [bug 1144910]
Affects: epel-6 [bug 1046628]
Red Hat Product Security has rated this issue as having Low security impact. This issue is not currently planned to be addressed in future updates. For additional information, refer to the Issue Severity Classification: https://access.redhat.com/security/updates/classification/.