Hi there,
Just posting here in case anyone else has been able to get /_layouts/15/OAuthAuthorize.aspx to work lately? A few days ago when trying to Auth Client ID's an error started occurring:

Sorry, something went wrong
There is no claims identity. Please make sure the web application is configured to use Claims Authentication.
URL used was in this form:
Have not been able to get any of our Client ID's or tenants working.
If anyone has a solution or a workaround, please let me know.
Cheers,
James.