I have emailed support@getfiddler.com and they have created an account for community.getfiddler.com, who would I need to contact to get SSO working? 

I've also tried signing in with Google which successfully logs in the browser but the app redirect "Go back To App" doesn't actually redirect me correctly, rather it still needs authentication for the Desktop app as if stuck in a loop forever. 

Update: Solution provided by Nick Iliev https://community.getfiddler.com/support/discussions/topics/12000027624 
Thanks!