ok , so , i will explain how to debug the things
First delete the obarun key by
# pacman-key -d 6DD4217456569BA711566AC7F06E8FDE7B45DAAC
then import it again
# sudo pacman-key --recv-keys 6DD4217456569BA711566AC7F06E8FDE7B45DAAC
now check the fingerprint
# sudo pacman-key --finger 6DD4217456569BA711566AC7F06E8FDE7B45DAAC
you should have this in front of you
pub rsa2048 2015-12-31 [SC] [expire : 2020-08-29]
6DD4 2174 5656 9BA7 1156 6AC7 F06E 8FDE 7B45 DAAC
uid [ inconnue] Eric Vidal (Obarun Key) <eric@ obarun.org>
sub rsa2048 2015-12-31 [E] [expire : 2020-08-29]
note the expiration date
now sign it localy by
# sudo pacman-key --lsign-key 6DD4217456569BA711566AC7F06E8FDE7B45DAAC
finally, enable again the check of gpg key for packages and databases in your pacman.conf like this
[obarun-testing]
SigLevel = Required
Server = https://repo.obarun.org/$arch/testing
[obarun]
SigLevel = Required
Server = https://repo.obarun.org/$arch
check if all it's good with
# pacman -Syy
So , now, this key will be revoked on the next update of obarun-keyring and replacing by a new one. This should be done automaticaly without any intervention of user.
Please, please, please, if you find something wrong make a feedback, thanks by advance