Generate token with random prefix

Added getitem function for specific item
- that decrypt is not invoked for previous run of the server
- and that server restart always triggers a client update

MinecraftDiscordBot/TimeoutTokenProvider.cs

@@ -1,13 +1,17 @@
 namespace MinecraftDiscordBot;
 
 public class TimeoutTokenProvider : ITokenProvider {
-    public TimeoutTokenProvider(int timeoutSeconds, ICipher? cipher = null) {
+    public TimeoutTokenProvider(int instanceId, int timeoutSeconds, ICipher? cipher = null) {
+        InstancePrefix = Convert.ToHexString(BitConverter.GetBytes(instanceId));
         _timeout = timeoutSeconds;
         _cipher = cipher ?? new AesCipher();
     }
     private readonly ICipher _cipher;
     private readonly int _timeout;
+    public string InstancePrefix { get; }
     public bool VerifyToken(string token) {
+        if (!token.StartsWith(InstancePrefix)) return false;
+        token = token[InstancePrefix.Length..];
         byte[] data;
         try {
             data = _cipher.Decrypt(Convert.FromHexString(token));
@@ -21,7 +25,7 @@ public class TimeoutTokenProvider : ITokenProvider {
     public string GenerateToken() {
         var time = BitConverter.GetBytes(DateTime.UtcNow.ToBinary());
         var key = Guid.NewGuid().ToByteArray();
-        var token = Convert.ToHexString(_cipher.Encrypt(time.Concat(key).ToArray()));
+        var token = InstancePrefix + Convert.ToHexString(_cipher.Encrypt(time.Concat(key).ToArray()));
         return token;
     }
 }