feature(#22): this commit introduces a handler to retrieve secrets from the realm

Author: https-richardy

Applications/Backend/Source/HttpsRichardy.Federation.Application/Handlers/Secret/FetchRealmSecretsHandler.cs

@@ -0,0 +1,20 @@
+namespace HttpsRichardy.Federation.Application.Handlers.Secret;
+
+public sealed class FetchRealmSecretsHandler(ISecretCollection collection) :
+    IDispatchHandler<FetchRealmSecretsParameters, Result<IReadOnlyCollection<SecretScheme>>>
+{
+    public async Task<Result<IReadOnlyCollection<SecretScheme>>> HandleAsync(
+        FetchRealmSecretsParameters parameters, CancellationToken cancellation = default)
+    {
+        var filters = SecretFilters.WithSpecifications()
+            .WithRealm(parameters.RealmId)
+            .Build();
+
+        var secrets = await collection.GetSecretsAsync(filters, cancellation);
+        var schemes = secrets.Select(secret => secret.AsResponse())
+            .ToList()
+            .AsReadOnly();
+
+        return Result<IReadOnlyCollection<SecretScheme>>.Success(schemes);
+    }
+}