Comment 8 for bug 1192704

With the client flow, there is no need to use the client secret, so you don't need to write it anywhere. You don't need to submit the new plugin to the account-plugins project, however I don't object to adding it here, if you want to. You certainly can use that project's plugins as a reference when writing yours.

As for the callback URL, it must be a valid URL. In most plugins we simply use https://wiki.ubuntu.com, just for convenience (the URL is not actually shown in the UI).