@0016f986 I don't think these web clients have authentication. They load as a web app in your browser, and you just login to your Mastodon account over API, like any other app. 

The trick would be restricting the web client to only connect to the desired Mastodon instance (and maybe including some 'branding' on the landing page so users know where they are). 

I'm sure this is possible, but I'm not sure the best way, or recommended, way to do it.