After adding a deployment key to a repo, I had to manually go to Admin panel, then running Rewrite '.ssh/authorized_keys' file. Then I was successfully authenticated again.
I created a new gogs user for my buildbot but I was unable to clone the user's own repos even though I had added the SSH key of my current UNIX user.
$ git clone ssh://firstname.lastname@example.org/buildbot/foobar.git Cloning into 'foobar'... Gogs: Key access denied fatal: Could not read from remote repository. Please make sure you have the correct access rights
I think one of my other gogs users was already registered with the same SSH key without my knowing. So it worked correctly after I created a new SSH key pair. (Be aware that the below command deletes a user's SSH keys and may be disastrous.)
$ sudo -u buildbot -i bash -l buildbot$ rm ~/.ssh/id_rsa ~/.ssh/id_rsa.pub buildbot$ ssh-keygen -b 4069 -t
Then the Gogs profile with the new public key
buildbot$ cat ~/.ssh/id_rsa.pub
And it all worked as expected again
$ git clone ssh://email@example.com/buildbot/foobar.git Cloning into 'foobar'... The authenticity of host '[git.example.com] ([ba:be:ca:fe::1337])' can't be established. RSA key fingerprint is SHA256:7xm2gVtHc41V0nh8NussuA7lNAzQwh5f9yn+5Mcpdmg. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added '[git.example.com],[ba:be:ca:fe::1337]' (RSA) to the list of known hosts. warning: You appear to have cloned an empty repository. Checking connectivity... done.
... I just have to confirm before posting a bug.