implemented Discord OAuth2

Lieb/Data/AccountController.cs

@@ -0,0 +1,32 @@
+using Microsoft.AspNetCore.Authentication;
+using Microsoft.AspNetCore.Authentication.Cookies;
+using Microsoft.AspNetCore.DataProtection;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Lieb.Data
+{
+    [Route("[controller]/[action]")] // Microsoft.AspNetCore.Mvc.Route
+    public class AccountController : ControllerBase
+    {
+        public IDataProtectionProvider Provider { get; }
+
+        public AccountController(IDataProtectionProvider provider)
+        {
+            Provider = provider;
+        }
+
+        [HttpGet]
+        public IActionResult Login(string returnUrl = "/")
+        {
+            return Challenge(new AuthenticationProperties { RedirectUri = returnUrl }, "Discord");
+        }
+
+        [HttpGet]
+        public async Task<IActionResult> Logout(string returnUrl = "/")
+        {
+            //This removes the cookie assigned to the user login.
+            await HttpContext.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
+            return LocalRedirect(returnUrl);
+        }
+    }
+}