Removes all references of System.Web.Security from core project

src/Umbraco.Web/StringExtensions.cs

@@ -0,0 +1,69 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Web.Security;
+
+namespace Umbraco.Web
+{
+    public static class StringExtensions
+    {
+        /// <summary>
+        /// Encrypt the string using the MachineKey in medium trust
+        /// </summary>
+        /// <param name="value">The string value to be encrypted.</param>
+        /// <returns>The encrypted string.</returns>
+        public static string EncryptWithMachineKey(this string value)
+        {
+            if (value == null)
+                return null;
+
+            string valueToEncrypt = value;
+            List<string> parts = new List<string>();
+
+            const int EncrpytBlockSize = 500;
+
+            while (valueToEncrypt.Length > EncrpytBlockSize)
+            {
+                parts.Add(valueToEncrypt.Substring(0, EncrpytBlockSize));
+                valueToEncrypt = valueToEncrypt.Remove(0, EncrpytBlockSize);
+            }
+
+            if (valueToEncrypt.Length > 0)
+            {
+                parts.Add(valueToEncrypt);
+            }
+
+            StringBuilder encrpytedValue = new StringBuilder();
+
+            foreach (var part in parts)
+            {
+                var encrpytedBlock = FormsAuthentication.Encrypt(new FormsAuthenticationTicket(0, string.Empty, DateTime.Now, DateTime.MaxValue, false, part));
+                encrpytedValue.AppendLine(encrpytedBlock);
+            }
+
+            return encrpytedValue.ToString().TrimEnd();
+        }
+
+        /// <summary>
+        /// Decrypt the encrypted string using the Machine key in medium trust
+        /// </summary>
+        /// <param name="value">The string value to be decrypted</param>
+        /// <returns>The decrypted string.</returns>
+        public static string DecryptWithMachineKey(this string value)
+        {
+            if (value == null)
+                return null;
+
+            string[] parts = value.Split('\n');
+
+            StringBuilder decryptedValue = new StringBuilder();
+
+            foreach (var part in parts)
+            {
+                decryptedValue.Append(FormsAuthentication.Decrypt(part.TrimEnd()).UserData);
+            }
+
+            return decryptedValue.ToString();
+        }
+    }
+}