The bkr client should have an option --proxy-user to make use of Beaker's "proxy user" feature. The intended usage is for scripts/bots which authenticate as a service account (which the admin has added to a Beaker group with proxy_user permission) and then perform actions on behalf of other users by passing --proxy-user <username>. Jan Stancek submitted a patch: http://gerrit.beaker-project.org/#/c/4035/
*** This bug has been marked as a duplicate of bug 1199853 ***