Reduce Unauthenticated Errors in Sentry (#238)

* Updated README to be explicit that kavita.db needs to be writable.

* Implemented a new Exception type that is for throwing a message to UI without logging in Sentry.

API/Extensions/ClaimsPrincipalExtensions.cs

@@ -1,4 +1,5 @@
 using System.Security.Claims;
+using Kavita.Common;
 
 namespace API.Extensions
 {
@@ -6,7 +7,9 @@ namespace API.Extensions
     {
         public static string GetUsername(this ClaimsPrincipal user)
         {
-            return user.FindFirst(ClaimTypes.NameIdentifier)?.Value;
+            var userClaim = user.FindFirst(ClaimTypes.NameIdentifier);
+            if (userClaim == null) throw new KavitaException("User is not authenticated");
+            return userClaim.Value;
         }
     }
 }

API/Program.cs

@@ -99,6 +99,7 @@ namespace API
                         options.AddExceptionFilterForType<OutOfMemoryException>();
                         options.AddExceptionFilterForType<NetVips.VipsException>();
                         options.AddExceptionFilterForType<InvalidDataException>();
+                        options.AddExceptionFilterForType<KavitaException>();
                         
                         options.BeforeSend = sentryEvent =>
                         {

Kavita.Common/KavitaException.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace Kavita.Common
+{
+    /// <summary>
+    /// These are used for errors to send to the UI that should not be reported to Sentry
+    /// </summary>
+    [Serializable]
+    public class KavitaException : Exception
+    {
+        public KavitaException()
+        {
+
+        }
+
+        public KavitaException(string message) : base(message)
+        {
+
+        }
+    }
+}

README.md

@@ -40,6 +40,7 @@ your reading collection with your friends and family!
 ## How to install
 - Unzip the archive for your target OS
 - Place in a directory that is writable. If on windows, do not place in Program Files
+- Linux users must ensure the directory & kavita.db is writable by Kavita (might require starting server once) 
 - Run Kavita
 - If you are updating, do not copy appsettings.json from the new version over. It will override your TokenKey and you will have to reauthenticate on your devices.