feat: Feature Provider Enhancements- #321 (#324)

This update focuses on enhancing the feature provider integration and
testing framework, incorporating improvements to flexibility, usability,
and testing capabilities.
This update addresses [GitHub Issue
#321](#321) in the
OpenFeature .NET SDK repository.

---

### Key Enhancements

1. **Dependency Injection (DI) Enhancements:**
   - Improved lifecycle management for better resource handling.
- Streamlined registration for feature providers, reducing configuration
complexity.
- Introduced the `AddProvider` extension method to simplify and adapt
feature provider integration during service setup.

2. **Simplified Codebase:**
- Removed `FeatureProviderFactory` logic, eliminating unnecessary
complexity and improving usability.

3. **Improved InMemoryProvider:**
- Enhanced the registration process for the `InMemoryProvider`, enabling
smoother and more intuitive usage.

4. **Testing Improvements:**
- Established a dedicated integration test project for comprehensive
validation.
- Improved overall test coverage, ensuring the reliability and
robustness of the framework.

---------

Signed-off-by: Artyom Tonoyan <arttonoyan@gmail.com>
Co-authored-by: chrfwow <christian.lutnik@dynatrace.com>

Directory.Packages.props

@@ -9,6 +9,7 @@
     <PackageVersion Include="Microsoft.Extensions.Hosting.Abstractions" Version="8.0.1" />
     <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.2" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="8.0.2" />
+    <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="8.0.1" />
     <PackageVersion Include="Microsoft.Extensions.Options" Version="8.0.2" />
     <PackageVersion Include="System.Collections.Immutable" Version="1.7.1" />
     <PackageVersion Include="System.Threading.Channels" Version="6.0.0" />
@@ -29,7 +30,7 @@
     <PackageVersion Include="SpecFlow.xUnit" Version="3.9.74" />
     <PackageVersion Include="xunit" Version="2.9.2" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.8.2" />
-    <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="8.0.1" />
+    <PackageVersion Include="Microsoft.AspNetCore.TestHost" Version="8.0.11" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(OS)' == 'Unix'">

OpenFeature.sln

@@ -85,6 +85,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "OpenFeature.DependencyInjec
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "OpenFeature.Hosting", "src\OpenFeature.Hosting\OpenFeature.Hosting.csproj", "{C99DA02A-3981-45A6-B3F8-4A1A48653DEE}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenFeature.IntegrationTests", "test\OpenFeature.IntegrationTests\OpenFeature.IntegrationTests.csproj", "{68463B47-36B4-8DB5-5D02-662C169E85B0}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -119,6 +121,10 @@ Global
 		{C99DA02A-3981-45A6-B3F8-4A1A48653DEE}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{C99DA02A-3981-45A6-B3F8-4A1A48653DEE}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{C99DA02A-3981-45A6-B3F8-4A1A48653DEE}.Release|Any CPU.Build.0 = Release|Any CPU
+		{68463B47-36B4-8DB5-5D02-662C169E85B0}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{68463B47-36B4-8DB5-5D02-662C169E85B0}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{68463B47-36B4-8DB5-5D02-662C169E85B0}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{68463B47-36B4-8DB5-5D02-662C169E85B0}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -137,6 +143,7 @@ Global
 		{C5415057-2700-48B5-940A-7A10969FA639} = {C97E9975-E10A-4817-AE2C-4DD69C3C02D4}
 		{EB35F9F6-8A79-410E-A293-9387BC4AC9A7} = {65FBA159-23E0-4CF9-881B-F78DBFF198E9}
 		{C99DA02A-3981-45A6-B3F8-4A1A48653DEE} = {C97E9975-E10A-4817-AE2C-4DD69C3C02D4}
+		{68463B47-36B4-8DB5-5D02-662C169E85B0} = {65FBA159-23E0-4CF9-881B-F78DBFF198E9}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {41F01B78-FB06-404F-8AD0-6ED6973F948F}

README.md

@@ -338,41 +338,43 @@ builder.Services.AddOpenFeature(featureBuilder => {
         });
 });
 ```
-#### Creating a New Provider
-To integrate a custom provider, such as InMemoryProvider, you’ll need to create a factory that builds and configures the provider. This section demonstrates how to set up InMemoryProvider as a new provider with custom configuration options.
 
-**Configuring InMemoryProvider as a New Provider**
-<br />Begin by creating a custom factory class, `InMemoryProviderFactory`, that implements `IFeatureProviderFactory`. This factory will initialize your provider with any necessary configurations.
-```csharp
-public class InMemoryProviderFactory : IFeatureProviderFactory
-{
-    internal IDictionary<string, Flag>? Flags { get; set; }
-
-    public FeatureProvider Create() => new InMemoryProvider(Flags);
-}
-```
-**Adding an Extension Method to OpenFeatureBuilder**
-<br />To streamline the configuration process, add an extension method, `AddInMemoryProvider`, to `OpenFeatureBuilder`. This allows you to set up the provider with either a domain-scoped or a default configuration.
+### Registering a Custom Provider
+You can register a custom provider, such as `InMemoryProvider`, with OpenFeature using the `AddProvider` method. This approach allows you to dynamically resolve services or configurations during registration.
 
 ```csharp
-public static partial class FeatureBuilderExtensions
-{
-    public static OpenFeatureBuilder AddInMemoryProvider(this OpenFeatureBuilder builder, Action<IDictionary<string, Flag>>? configure = null)
-        => builder.AddProvider<InMemoryProviderFactory>(factory => ConfigureFlags(factory, configure));
+services.AddOpenFeature()
+        .AddProvider(provider =>
+        {
+            // Resolve services or configurations as needed
+            var configuration = provider.GetRequiredService<IConfiguration>();
+            var flags = new Dictionary<string, Flag>
+            {
+                { "feature-key", new Flag<bool>(configuration.GetValue<bool>("FeatureFlags:Key")) }
+            };
+
+            // Register a custom provider, such as InMemoryProvider
+            return new InMemoryProvider(flags);
+        });
+```
 
-    public static OpenFeatureBuilder AddInMemoryProvider(this OpenFeatureBuilder builder, string domain, Action<IDictionary<string, Flag>>? configure = null)
-        => builder.AddProvider<InMemoryProviderFactory>(domain, factory => ConfigureFlags(factory, configure));
+#### Adding a Domain-Scoped Provider
 
-    private static void ConfigureFlags(InMemoryProviderFactory factory, Action<IDictionary<string, Flag>>? configure)
-    {
-        if (configure == null)
-            return;
+You can also register a domain-scoped custom provider, enabling configurations specific to each domain:
 
-        var flag = new Dictionary<string, Flag>();
-        configure.Invoke(flag);
-        factory.Flags = flag;
-    }
-}
+```csharp
+services.AddOpenFeature()
+        .AddProvider("my-domain", (provider, domain) =>
+        {
+            // Resolve services or configurations as needed for the domain
+            var flags = new Dictionary<string, Flag>
+            {
+                { $"{domain}-feature-key", new Flag<bool>(true) }
+            };
+
+            // Register a domain-scoped custom provider such as InMemoryProvider
+            return new InMemoryProvider(flags);
+        });
 ```
 
 <!-- x-hide-in-docs-start -->