Добавьте файлы проекта.

Yuna.OauthServer/Endpoints/Auth/DTO/AuthRequest.cs

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+using Microsoft.AspNetCore.Components;
+using System.Text.Json.Serialization;
+
+namespace Yuna.OauthServer.Endpoints.Auth.DTO
+{
+    
+    public class AuthRequest
+    {
+        public string response_type { get; set; } = null!;
+        public string client_id { get; set; } = null!;
+        public string redirect_uri { get; set; } = null!;
+
+    }
+}

Yuna.OauthServer/Endpoints/Auth/DTO/AuthResponse.cs

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+namespace Yuna.OauthServer.Endpoints.Auth.DTO
+{
+    public class AuthResponse
+    {
+        public string ResponseType { get;} = "code";
+        public string Code { get; set; } = null!;
+        public string RedirectUri { get; set; } = null!;
+    }
+}