Adds Default Targeting Accessor and extension method WithTargeting (#466)

* Adds default targeting accessor and extension method WithTargeting variation for ASP.NET

* Updates accessor to internal

* Forced query evaluation

* Updated description of .WithTargeting extension

Author: rossgrambo

examples/FeatureFlagDemo/Authentication/QueryStringAuthenticationHandler.cs

@@ -49,7 +49,7 @@ protected override Task<AuthenticateResult> HandleAuthenticateAsync()
 
                 foreach (string group in groups)
                 {
-                    identity.AddClaim(new Claim(ClaimTypes.GroupName, group));
+                    identity.AddClaim(new Claim(ClaimTypes.Role, group));
                 }
 
                 Logger.LogInformation($"Assigning the following groups '{string.Join(", ", groups)}' to the request.");

examples/FeatureFlagDemo/ClaimTypes.cs

@@ -45,7 +45,7 @@ public void ConfigureServices(IServiceCollection services)
 
             services.AddFeatureManagement()
                     .AddFeatureFilter<BrowserFilter>()
-                    .WithTargeting<HttpContextTargetingContextAccessor>()
+                    .WithTargeting()
                     .UseDisabledFeaturesHandler(new FeatureNotEnabledDisabledHandler());
 
             services.AddMvc(o =>

examples/FeatureFlagDemo/HttpContextTargetingContextAccessor.cs

@@ -3,9 +3,12 @@
 //
 using Microsoft.AspNetCore.Mvc.Filters;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.FeatureManagement.FeatureFilters;
 using Microsoft.FeatureManagement.Mvc;
 using System;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace Microsoft.FeatureManagement
 {
@@ -44,5 +47,28 @@ public static IFeatureManagementBuilder UseDisabledFeaturesHandler(this IFeature
 
             return builder;
         }
+
+        /// <summary>
+        /// Enables the use of targeting within the application and adds a targeting context accessor that extracts targeting details from a request's HTTP context.
+        /// </summary>
+        /// <param name="builder">The <see cref="IFeatureManagementBuilder"/> used to customize feature management functionality.</param>
+        /// <returns>A <see cref="IFeatureManagementBuilder"/> that can be used to customize feature management functionality.</returns>
+        public static IFeatureManagementBuilder WithTargeting(this IFeatureManagementBuilder builder)
+        {
+            //
+            // Register the targeting context accessor with the same lifetime as the feature manager
+            if (builder.Services.Any(descriptor => descriptor.ServiceType == typeof(IFeatureManager) && descriptor.Lifetime == ServiceLifetime.Scoped))
+            {
+                builder.Services.TryAddScoped<ITargetingContextAccessor, DefaultHttpTargetingContextAccessor>();
+            }
+            else
+            {
+                builder.Services.TryAddSingleton<ITargetingContextAccessor, DefaultHttpTargetingContextAccessor>();
+            }
+
+            builder.AddFeatureFilter<TargetingFilter>();
+
+            return builder;
+        }
     }
 }

examples/FeatureFlagDemo/Startup.cs

@@ -0,0 +1,74 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Microsoft.AspNetCore.Http;
+using Microsoft.FeatureManagement.FeatureFilters;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Security.Claims;
+using System.Threading.Tasks;
+
+namespace Microsoft.FeatureManagement
+{
+    /// <summary>
+    /// Provides a default implementation of <see cref="ITargetingContextAccessor"/> that creates <see cref="TargetingContext"/> using info from the current HTTP request.
+    /// </summary>
+    internal sealed class DefaultHttpTargetingContextAccessor : ITargetingContextAccessor
+    {
+        /// <summary>
+        /// The key used to store and retrieve the <see cref="TargetingContext"/> from the <see cref="HttpContext"/> items.
+        /// </summary>
+        private static object _cacheKey = new object();
+
+        private readonly IHttpContextAccessor _httpContextAccessor;
+
+        /// <summary>
+        /// Creates an instance of the DefaultHttpTargetingContextAccessor
+        /// </summary>
+        public DefaultHttpTargetingContextAccessor(IHttpContextAccessor httpContextAccessor)
+        {
+            _httpContextAccessor = httpContextAccessor ?? throw new ArgumentNullException(nameof(httpContextAccessor));
+        }
+
+        /// <summary>
+        /// Gets <see cref="TargetingContext"/> from the current HTTP request.
+        /// </summary>
+        public ValueTask<TargetingContext> GetContextAsync()
+        {
+            HttpContext httpContext = _httpContextAccessor.HttpContext;
+
+            //
+            // Try cache lookup
+            if (httpContext.Items.TryGetValue(_cacheKey, out object value))
+            {
+                return new ValueTask<TargetingContext>((TargetingContext)value);
+            }
+
+            //
+            // Treat user identity name as user id
+            ClaimsPrincipal user = httpContext.User;
+
+            string userId = user?.Identity?.Name;
+
+            //
+            // Treat claims of type Role as groups
+            IEnumerable<string> groups = httpContext.User.Claims
+                .Where(c => c.Type == ClaimTypes.Role)
+                .Select(c => c.Value)
+                .ToList();
+
+            TargetingContext targetingContext = new TargetingContext
+            {
+                UserId = userId,
+                Groups = groups
+            };
+
+            //
+            // Cache for subsequent lookup
+            httpContext.Items[_cacheKey] = targetingContext;
+
+            return new ValueTask<TargetingContext>(targetingContext);
+        }
+    }
+}