WKD support
This MR adds support for Hagrid to act as a WKD gateway.
The idea is that mail hosts can point a CNAME record on their openpgpkey
subdomain to wkd.keys.openpgp.org
. Hagrid serves keys for verified addresses under .well-known/openpgpkey/DOMAIN/hu/ZBASE32(SHA1(LOCALPART))
, in keeping with the WKD "advanced" method.
Edited by Vincent Breitmoser