csr_id is exposed over HTTPS with short living self signed certificate,
which is transmitted via SlapOS Master. Thanks to this, it is possible to
match csr_id with certificate of given partition and take decision if it shall
be signed or not.

This is "quite secure" apporach, a bit better than blidny trusting what CSR
to sign in KeDiFa. The bootstrap information, which is short living
(certificates are valid for 5 days), resides in SlapOS Master. The csr_id
is not directly known to SlapOS Master, and shall be consumed as fast as
possible by frontend cluster operator in order to sign CSR appearing in
KeDiFa caucase. The known possible attack vector requires that attacker knows
caucased HTTP listening port and can hijack HTTPS traffic to the csr_id-url
to get the human approve his own csr_id. The second is hoped to be overcomed
by publishing certificate of this endpoint via SlapOS Master.

Unfortunately caucase-updater prefix is directly used to find real CSR, as the
one generated is just a template for rerequest, thus csr_id would be different
from really used by caucase-updater.