Squashed commit of ASF 2FA

Check https://github.com/JustArchi/ArchiSteamFarm/wiki/Escrow for more info

SteamAuth/Util.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Net;
+
+namespace SteamAuth
+{
+    public class Util
+    {
+        public static long GetSystemUnixTime()
+        {
+            return (long)(DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1))).TotalSeconds;
+        }
+
+        public static byte[] HexStringToByteArray(string hex)
+        {
+            int hexLen = hex.Length;
+            byte[] ret = new byte[hexLen / 2];
+            for (int i = 0; i < hexLen; i += 2)
+            {
+                ret[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
+            }
+            return ret;
+        }
+    }
+}