expose time provider for TimeWindowFilter

Author: zhiyuanliang-ms

src/Microsoft.FeatureManagement/FeatureFilters/TimeWindowFilter.cs

@@ -37,9 +37,9 @@ public TimeWindowFilter(ILoggerFactory loggerFactory = null)
         public IMemoryCache Cache { get; set; }
 
         /// <summary>
-        /// This property allows the time window filter in our test suite to use simulated time.
+        /// This property allows the time window filter to use custom <see cref="TimeProvider"/>.
         /// </summary>
-        internal TimeProvider SystemClock { get; set; }
+        public TimeProvider SystemClock { get; set; }
 
         /// <summary>
         /// Binds configuration representing filter parameters to <see cref="TimeWindowFilterSettings"/>.

src/Microsoft.FeatureManagement/ServiceCollectionExtensions.cs

@@ -175,7 +175,8 @@ private static IFeatureManagementBuilder GetFeatureManagementBuilder(IServiceCol
             builder.AddFeatureFilter<TimeWindowFilter>(sp =>
                 new TimeWindowFilter()
                 {
-                    Cache = sp.GetRequiredService<IMemoryCache>()
+                    Cache = sp.GetRequiredService<IMemoryCache>(),
+                    SystemClock = sp.GetService<TimeProvider>() ?? TimeProvider.System,
                 });
 
             builder.AddFeatureFilter<ContextualTargetingFilter>();