Add option for no feature management section found

src/Microsoft.FeatureManagement/ConfigurationFeatureDefinitionProvider.cs

@@ -27,8 +27,8 @@ sealed class ConfigurationFeatureDefinitionProvider : IFeatureDefinitionProvider
         private const string FeatureManagementSectionName = "FeatureManagement";
         private readonly IConfiguration _configuration;
         private readonly ConcurrentDictionary<string, FeatureDefinition> _definitions;
-        private IDisposable _changeSubscription;
         private readonly ILogger _logger;
+        private IDisposable _changeSubscription;
         private int _stale = 0;
 
         public ConfigurationFeatureDefinitionProvider(IConfiguration configuration, ILoggerFactory loggerFactory)
@@ -42,6 +42,11 @@ public ConfigurationFeatureDefinitionProvider(IConfiguration configuration, ILog
                 () => _stale = 1);
         }
 
+        /// <summary>
+        /// The option that controls the behavior when "FeatureManagement" section in the configuration is missing.
+        /// </summary>
+        public bool UseTopLevelConfiguration { get; init; }
+
         public void Dispose()
         {
             _changeSubscription?.Dispose();
@@ -217,6 +222,13 @@ private IEnumerable<IConfigurationSection> GetFeatureDefinitionSections()
                 return featureManagementConfigurationSection.GetChildren();
             }
 
+            //
+            // There is no "FeatureManagement" section in the configuration
+            if (UseTopLevelConfiguration)
+            {
+                return _configuration.GetChildren();
+            }
+
             _logger.LogDebug($"No configuration section named '{FeatureManagementSectionName}' was found.");
 
             return Enumerable.Empty<IConfigurationSection>();

src/Microsoft.FeatureManagement/ServiceCollectionExtensions.cs

@@ -69,6 +69,7 @@ public static IFeatureManagementBuilder AddFeatureManagement(this IServiceCollec
 
         /// <summary>
         /// Adds singleton <see cref="FeatureManager"/> and other required feature management services.
+        /// The registered <see cref="ConfigurationFeatureDefinitionProvider"/> will use the provided configuration and read from the top level if no "FeatureManagement" section can be found.
         /// </summary>
         /// <param name="services">The service collection that feature management services are added to.</param>
         /// <param name="configuration">A specific <see cref="IConfiguration"/> instance that will be used to obtain feature settings.</param>
@@ -80,7 +81,13 @@ public static IFeatureManagementBuilder AddFeatureManagement(this IServiceCollec
                 throw new ArgumentNullException(nameof(configuration));
             }
 
-            services.AddSingleton<IFeatureDefinitionProvider>(sp => new ConfigurationFeatureDefinitionProvider(configuration, sp.GetRequiredService<ILoggerFactory>()));
+            services.AddSingleton<IFeatureDefinitionProvider>(sp =>
+                new ConfigurationFeatureDefinitionProvider(
+                    configuration,
+                    sp.GetRequiredService<ILoggerFactory>())
+                {
+                    UseTopLevelConfiguration = true
+                });
 
             return services.AddFeatureManagement();
         }
@@ -135,6 +142,7 @@ public static IFeatureManagementBuilder AddScopedFeatureManagement(this IService
 
         /// <summary>
         /// Adds scoped <see cref="FeatureManager"/> and other required feature management services.
+        /// The registered <see cref="ConfigurationFeatureDefinitionProvider"/> will use the provided configuration and read from the top level if no "FeatureManagement" section can be found.
         /// </summary>
         /// <param name="services">The service collection that feature management services are added to.</param>
         /// <param name="configuration">A specific <see cref="IConfiguration"/> instance that will be used to obtain feature settings.</param>
@@ -146,7 +154,13 @@ public static IFeatureManagementBuilder AddScopedFeatureManagement(this IService
                 throw new ArgumentNullException(nameof(configuration));
             }
 
-            services.AddSingleton<IFeatureDefinitionProvider>(sp => new ConfigurationFeatureDefinitionProvider(configuration, sp.GetRequiredService<ILoggerFactory>()));
+            services.AddSingleton<IFeatureDefinitionProvider>(sp =>
+                new ConfigurationFeatureDefinitionProvider(
+                    configuration,
+                    sp.GetRequiredService<ILoggerFactory>())
+                {
+                    UseTopLevelConfiguration = true
+                });
 
             return services.AddScopedFeatureManagement();
         }

tests/Tests.FeatureManagement/FeatureManagement.cs

@@ -72,8 +72,7 @@ public async Task ReadsOnlyFeatureManagementSection()
 
             services
                 .AddSingleton(config)
-                .AddFeatureManagement()
-                .AddFeatureFilter<TestFilter>();
+                .AddFeatureManagement();
 
             ServiceProvider serviceProvider = services.BuildServiceProvider();
 
@@ -87,6 +86,26 @@ public async Task ReadsOnlyFeatureManagementSection()
             }
         }
 
+        [Fact]
+        public async Task ReadsTopLevelConfiguration()
+        {
+            const string feature = "FeatureX";
+
+            var stream = new MemoryStream(Encoding.UTF8.GetBytes($"{{\"AllowedHosts\": \"*\", \"FeatureFlags\": {{\"{feature}\": true}}}}"));
+
+            IConfiguration config = new ConfigurationBuilder().AddJsonStream(stream).Build();
+
+            var services = new ServiceCollection();
+
+            services.AddFeatureManagement(config.GetSection("FeatureFlags"));
+
+            ServiceProvider serviceProvider = services.BuildServiceProvider();
+
+            IFeatureManager featureManager = serviceProvider.GetRequiredService<IFeatureManager>();
+
+            Assert.True(await featureManager.IsEnabledAsync(feature));
+        }
+
         [Fact]
         public void AddsScopedFeatureManagement()
         {