information on FQDN based authentication between client and server.

keshavshor4, ok, if I get this right, you're working on the external auth provider implementation and would like to use an FQDN as a redirect URI. You generally set this up in the Active Directory, register the auth providers and your app, verify a domain name, and set it as a Redirect URI. More about this configuration https://docs.microsoft.com/en-us/azure/app-service/configure-authentication-provider-aad.

Debugging the app locally is not a big deal. Generally, the approach is spinning around configuring your 'hosts' file, which is well-described https://docs.microsoft.com/en-us/aspnet/web-api/overview/security/external-authentication-services.

Hope that helps