You can’t use put_flash when using the sign_in tokens, if the failure was a “normal” failure. What I mean by this is that the sign in action submits the form and shows any errors, and if there were things like validation errors or anything standard like that, it just displays them. Is your log level configured low enough? Try setting it to debug to see if any errors come through. Otherwise, you can turn off sign_in_tokens and see what the failure is, which it sounds like you did.
What failure are you seeing? I’m not sure what you mean about identity_name, but @jimsynz might be able to give you pointers on that front. What do you need the identity_name for? What is the nature of the failure?
On your resource, do you have policies?