Enhance login page with improved UI and error handling for invalid credentials

FoodsharingSiegen.Server/Pages/Login.razor.cs

@@ -33,6 +33,11 @@ namespace FoodsharingSiegen.Server.Pages
         /// </summary>
         private string? Password { get; set; }
 
+        /// <summary>
+        ///     Gets or sets the login error message
+        /// </summary>
+        private string? LoginErrorMessage { get; set; }
+
         #endregion
 
         #region Private Method PerformLogin
@@ -42,12 +47,14 @@ namespace FoodsharingSiegen.Server.Pages
         /// </summary>
         private async Task PerformLogin()
         {
+            LoginErrorMessage = null;
             //Todo Eingaben Validieren [04.04.22 - Andre Beging]
 
             if (string.IsNullOrWhiteSpace(MailAddress) || string.IsNullOrWhiteSpace(Password))
             {
                 MailAddress = string.Empty;
                 Password = string.Empty;
+                LoginErrorMessage = "E-Mail-Adresse oder Passwort ist ungültig.";
                 return;
             }
 
@@ -55,7 +62,7 @@ namespace FoodsharingSiegen.Server.Pages
             if (loginR.Success)
                 NavigationManager.NavigateTo("/", true);
             else
-                await Notification.Error(loginR.ErrorMessage)!;
+                LoginErrorMessage = "E-Mail-Adresse oder Passwort ist ungültig.";
         }
 
         #endregion