[Prototype] Add multitenant version of dynamic schemes sample

[HaoK]

So early cut of the multi-tenant + auth options sample.

I took the existing dynamic schemes samples and made it work for different tenants, I just used a lame
?tenant=id query string to simulate different tenants.

The sample has adds these services:

            // Just returns the tenant id
            services.AddSingleton<TenantResolver>();

            // Basically adds a layer of tenant to named options dictionary
            services.AddSingleton<IOptionsMonitor<SimpleOptions>, TenantOptionsMonitor>();

            // These are needed to be able to add/remove schemes and also update their options
            services.AddSingleton<IAuthenticationSchemeProvider, TenantSchemeResolver>();
            services.AddSingleton<TenantOptionsCache>();

The result is each tenant has its own set of authentication schemes and options configurations, and can be updated dynamically using /?tenant=id

Thoughts @Tratcher @davidfowl @blowdart

[blowdart]

Interface rather than class? That way we could push a database into it, so people can map from config in a database

[HaoK]

So this isn't something we are shipping, this is just a sample, so there's not really much upside for an interface in the sample when they would just modify this to take any dependencies needed, if they wanted it to use a DbContext, they could just make it Scoped, although that would affect the lifetimes of the other things too

[Tratcher]

Looks promising. It's hard to call this a supported scenario when you have to implement this many types.

[Tratcher]

Also TenantSchemeResolver and company

[HaoK]

Yeah i still need to update the readmes

[Tratcher]

Why aren't these needed?

[HaoK]

This sample doesn't actually do auth, the pages just list the schemes and their creds. Its just demonstrating how you configure different schemes in different tenants, its not functionally using auth.

[HaoK]

hence its Options.Multitenant as opposed to Auth.Multitenant

[HaoK]

But basically this implementation doesn't support defaults, which makes sense since they hang off the singleton AuthenticationOptions anyways

[HaoK]

But yeah this certainly isn't 'easy', but its doable via extensibility (not sure what the definition of 'supported' is)

[HaoK]

Any major concerns with this sample? If not I'll add some tests and call it good enough for now

[Tratcher]

No, go ahead.

[Tratcher]

Rebase? you picked up a lot of extra commits.

[natemcmaster]

This repo is about to be archived. AuthSamples are now part of aspnet/AspNetCore.

cref dotnet/aspnetcore#4088