I finally got a chance to do this (other priorities more pressing!) but it's not working for me.
I've been using the Moodle Mobile app with password authentication with no problems but just installed the additional features plugin. Now I can't log in from the app at all.
I've double-checked my configuration of the plugin, and checked the SSL certificate, etc. and also restarted the web server. On my phone, I've force-stopped the app, deleted its data and deleted its cache. But no matter what I do, when I connect to my site, I get prompted for Username and Password above a blue "Log In" button. There's no option to use a Google account (which I've been doing for years on the site), and if I tap "Log In" it complains about no username, and if I put in my email address it complains that it needs a password. If I provide the password - and I've reset and double-checked the password - I still get "Invalid login, please retry".
Moodle v 3.1.5 (will do 3.1.6 upgrade once I've got this sorted out), Moodle Mobile app v 3.3, OAuth 2 plugin 2.3, Mobile additional features 3.1.321.
I suspect that the inability to log in is because I have two accounts with the same email address - one that was created using OAuth2 and one that uses password authentication. When I try to log in from the app, it's finding the first account which uses OAuth2 - but it's not activating a browser or doing anything other than straight password authentication, which won't work.
How is this supposed to work? Where does the user get to choose OAuth2 authentication?
I'm totally lost, now and will just have to disable this plugin.
Update: scratch that! I just scrolled back up the installation instructions and found the needed step:
'Once the plugin is installed, you need to go to Site administration
> Plugins > Local plugins > Moodle Mobile additional features
There you can choose the "Type of login'
Once I'd done that, everything started working. I'm a happy camper again!