I don't know what should I enter for callback URL.
When I make OAuth Apps, I have to enter callback URL, so I write http:// my-node-red-url(localhost) :1880/auth/strategy/callback/.
It's on Setting up node-red-auth-github
But I get error, <AuthorizationError: The redirect_uri MUST match the registered callback URL for this application.>
Also, you won't be able to use "localhost" in the callback URL - it will need to be a publicly available URL. If you are running this at home you'll need to have a registered domain and DNS records that associate the domain name with either a static IP address or using a dynamic ip address provider like DynDNS set up in your router.