Is it no longer possible to use Oauth without having a redirect URI?

Is it no longer possible to use Oauth without having a redirect URI?

Oauth has been working fine for about a year. Unfortunately the secret expired in azure. I update the secret but email no longer works. checked the app registration settings in azure and almost everything is blank to include permissions. No idea how it continued to work until today. 

The issue I am having is that in the past the redirect URI was optional. now it seems like it is mandatory and we don't want to make ServiceDesk accessible on the internet. Is there any way to get around this? 
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