Adds Default Targeting Accessor and extension method WithTargeting

[rossgrambo]

Why this PR?

1. Addresses issues
   a. Add Default Http Targeting Context Accessor #415
2. Updates FeatureFlagDemo example to use the new extension

Visible Changes

Developers using ASP.NET will now have a new extension method available to them, WithTargeting(). Previously, they could only use WithTargeting<ITargetingContextAccessor>()

builder.Services.AddFeatureManagement()
    .WithTargeting()

This default accessor will extract the targeting info from HttpContext.User. Groups will be extracted from claims of type Role. UserId is taken from the Identity.Name field.

[zhiyuanliang-ms]

Should we call AddHttpContextAccessor in this method since our default targeting accessor depends on it.

[rossgrambo]

That's a great question. I originally thought no- so we're in parity with what we have today. However it would remove another hurdle to get started so I think it's a good idea.

[jimmyca15]

I'd like to decouple that.

By the way, is this method name the one that we discussed so many options and couldn't settle on one?

[rossgrambo]

Okay, let's keep it decoupled. Could always do that in a separate PR anyway.

By the way, is this method name the one that we discussed so many options and couldn't settle on one?

Yes it is. The last design review it was discussed up was the caching meeting last month. We lightly aligned on .WithTelemetry<DefaultTargetingContextAccessor>(), but some smaller discussion afterwards lead to .WithTelemetry() so we didn't have to make DefaultTargetingContextAccessor public.

Although I'm having trouble finding a paper trail to confirm that we did commit to this.

[rossgrambo]

@zhenlan do you have thoughts on the .WithTelemetry() WithTargeting() over .WithTargeting<DefaultTargetingContextAccessor>()

[jimmyca15]

Yes, this would have been referring to WithTargeting, not WithTelemetry

[jimmyca15]

Would a blazor user take a dependency on this package and see this method? My thought is that if we go with WithTargeting, any application that would depend on this package should most likely use this method.

[rossgrambo]

My fault- yes .WithTargeting.

Blazor Webassembly is just a client side thing- so it would work fine with an ASP.NET backend requiring this.

Blazor Server would not work as expected- and I wouldn't expect the dev to use the ASP.NET package. Although- Blazor Server are built on top of ASP.NET Core so it's not unreasonable a developer would try this.

[zhenlan]

We could add it by default if 1) it will not break any existing applications and 2) users can easily override it if they want to use their own targeting context accessor.

[jimmyca15]

Okay, having it with just WithTargeting sounds reasonable to me.

[zhiyuanliang-ms]

This is a new feature. After this is released, we need to update our public doc to introduce it.

[jimmyca15]

That's an internal type. It shouldn't show up in a public method summary. The compiler allows it?

[jimmyca15]

Since DefaultHttpTargetingContextAccessor is internal, users won't see its class summary so some of those details would be useful here.

[rossgrambo]

Good point- how about:

Suggested change

	/// Adds the <see cref="DefaultHttpTargetingContextAccessor"/> to be used for targeting and registers the targeting filter to the feature management system.
	/// Adds the default ASP.NET <see cref="ITargetingContextAccessor"/> to be used for targeting and registers the targeting filter to the feature management system.

?

[jimmyca15]

I would say something like.

Enables the use of targeting within the application and adds a targeting context accessor that extracts targeting details from a request's HTTP context.

[zhiyuanliang-ms]

@jimmyca15 @rossgrambo After this PR is merged, I think we can publish a new stable release. What do you think?

[rossgrambo]

Sounds good to me.

There was an issue with the build not starting. Should be fixed now, so I'll merge shortly.