Recommended alternative to Windows Authentication

RE: "Windows Authentication (NTLM/Kerberos/Negotiate) can't be used with gRPC"

I've not been able to find any information on what the recommended alternative to using Windows Authentication is. I need something that:
* Can be used from a desktop app
* Is (largely) transparent to the user
* Provides per-user authentication & authorization
* _Can be used when the entire domain is not attached to the internet_. (Does this rule out Azure AD?)

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#### Document Details

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* ID: 363b40bb-4e20-e4b3-4456-5eb8fe6b30fb
* Version Independent ID: 8a7e85b0-5c1c-969d-9748-5e5e2dc45cce
* Content: [Authentication and authorization in gRPC for ASP.NET Core](https://docs.microsoft.com/en-us/aspnet/core/grpc/authn-and-authz?view=aspnetcore-3.0#feedback)
* Content Source: [aspnetcore/grpc/authn-and-authz.md](https://github.com/aspnet/AspNetCore.Docs/blob/master/aspnetcore/grpc/authn-and-authz.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-grpc**
* GitHub Login: @JamesNK
* Microsoft Alias: **jamesnk**