I store them in a password store[0], encrypted to my GPG key. That store is itself a git repo, which is encrypted to the same key using git-remote-gcrypt and synced with a remote server.

Thus I can run something like:

    $ pass foobar.example
    jDHQxFTkPjLkvbLNRQe5Ad

Or:

    $ pass -c bazquux.example
    Copied bazquux.example to clipboard. Will clear in 45 seconds.

[0] https://www.passwordstore.org/