There is some real legacy to the login process in this app. It includes redirection over a third party which is, frankly, not something I want to use.
Thankfully @flypig demonstrated how to do oath against the mastodon apis here: Sailfish Community News, 2nd December, Developer Docs, WebAuth … Now to implement it with tooter toot, di toot. Or hope @flypig beats me too it 
In any case, the ‘modern’ WebView works and it’s a lot nicer rendering.