Hi David,
I thought I was making progress then I hit against yet another problem! This time it’s to do with Cookies and it would seem that OmniAuth is trying to store the entire JWT response which is too long. To be honest it could be something to do with what I’ve done but I can’t make any further progress as this is too deep into RoR for me 
ActionDispatch::Cookies::CookieOverflow (ActionDispatch::Cookies::CookieOverflow)
/var/www/discourse/vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.0/lib/action_dispatch/middleware/cookies.rb:649:in `commit’
Any advice would be appreciated before I throw in the towel with this one..
Thanks
Andy