Starting today, the Debian Repository Key of the Owncloud Repository expired. My setup is according to this manual: https://download.owncloud.org/download/repositories/stable/owncloud/index.html
To check the expiration date I used this command:
$ wget -q https://download.owncloud.org/download/repositories/production/Debian_9.0/Release.key -O - | gpg - gpg: WARNING: no command supplied. Trying to guess what you mean ... pub rsa2048 2013-08-26 [SC] [expired: 2018-08-25] DDA2C105C4B73A6649AD2BBD47AE7F72479BC94B uid ownCloud build service <obsrun@localhost> sub rsa2048 2013-08-26 [E] [expired: 2018-08-25] sub dsa2048 2013-08-26 [S] [expired: 2018-08-25] sub elg2048 2013-08-26 [E] [expired: 2018-08-25]
Please extend the key or provide a new one and notify us here in the thread, that we can fix this issue on our server.