Adds Argon2 for password protection (#123)

Projects/Argon2/Argon2Exception.cs

@@ -0,0 +1,20 @@
+using System;
+
+namespace Server.Accounting.Security
+{
+  /// <summary>
+  /// An exception class to wrap the errors returned by Daniel Dinu and Dmitry Khovratovich's Argon2 library.
+  ///
+  /// Except through very unusual conditions, the only exceptions which could be thrown from PasswordHasher
+  /// are Argon2Exception, ArgumentNullException, DllNotFoundException (if libargon2.dll is not found)
+  /// </summary>
+  public class Argon2Exception : Exception
+  {
+    /// <summary>
+    /// Construct an Argon2Exception with the specified Argon2 error code
+    /// <param name="action">Which method the Argon2Exception originated from</param>
+    /// <param name="error">The error returned from the Argon2 library</param>
+    /// </summary>
+    public Argon2Exception(string action, Argon2Error error) : base(string.Format("Error during Argon2 {0}: ({1}) {2}", action, (int)error, error)) {}
+  }
+}