Add DynamicClientStore (#5670)

* Add DynamicClientStore

* Formatting

* Fix Debug assertion

* Make Identity internals visible to its unit tests

* Add installation client provider tests

* Add internal client provider tests

* Add DynamicClientStore tests

* Fix namespaces after merge

* Format

* Add docs and remove TODO comments

* Use preferred prefix for API keys

---------

Co-authored-by: Jared Snider <116684653+JaredSnider-Bitwarden@users.noreply.github.com>

src/Identity/IdentityServer/ServiceCollectionExtensions.cs

@@ -0,0 +1,28 @@
+using Bit.Identity.IdentityServer;
+
+namespace Microsoft.Extensions.DependencyInjection;
+
+public static class ServiceCollectionExtensions
+{
+    /// <summary>
+    /// Registers a custom <see cref="IClientProvider"/> for the given identifier to be called when a client id with
+    /// the identifier is attempting authentication.
+    /// </summary>
+    /// <typeparam name="T">Your custom implementation of <see cref="IClientProvider"/>.</typeparam>
+    /// <param name="services">The service collection to add services to.</param>
+    /// <param name="identifier">
+    /// The identifier to be used to invoke your client provider if a <c>client_id</c> is prefixed with your identifier
+    /// then your <see cref="IClientProvider"/> implementation will be invoked with the data after the seperating <c>.</c>.
+    /// </param>
+    /// <returns>The <see cref="IServiceCollection"/> for additional chaining.</returns>
+    public static IServiceCollection AddClientProvider<T>(this IServiceCollection services, string identifier)
+        where T : class, IClientProvider
+    {
+        ArgumentNullException.ThrowIfNull(services);
+        ArgumentException.ThrowIfNullOrWhiteSpace(identifier);
+
+        services.AddKeyedTransient<IClientProvider, T>(identifier);
+
+        return services;
+    }
+}