add error handler middleware

Foxchat.Identity/Middleware/AuthorizationMiddleware.cs

@@ -0,0 +1,37 @@
+using Foxchat.Core;
+using Foxchat.Identity.Database;
+using NodaTime;
+
+namespace Foxchat.Identity.Middleware;
+
+public class AuthorizationMiddleware(
+    IdentityContext db,
+    IClock clock
+) : IMiddleware
+{
+    public async Task InvokeAsync(HttpContext ctx, RequestDelegate next)
+    {
+        var endpoint = ctx.GetEndpoint();
+        var attribute = endpoint?.Metadata.GetMetadata<AuthorizeAttribute>();
+
+        if (attribute == null)
+        {
+            await next(ctx);
+            return;
+        }
+
+        var token = ctx.GetToken();
+        if (token == null || token.Expires > clock.GetCurrentInstant())
+            throw new ApiError.Unauthorized("This endpoint requires an authenticated user.");
+        if (attribute.Scopes.Length > 0 && attribute.Scopes.Except(token.Scopes).Any())
+            throw new ApiError.Forbidden("This endpoint requires ungranted scopes.", attribute.Scopes.Except(token.Scopes));
+
+        await next(ctx);
+    }
+}
+
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
+public class AuthorizeAttribute(params string[] scopes) : Attribute
+{
+    public readonly string[] Scopes = scopes;
+}