Machine Key Section validation and decryption key rotation on build

GenerateMachineKey.targets

<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <UsingTask
    TaskName="GenerateMachineKey"
    TaskFactory="CodeTaskFactory"
    AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll" >
    <ParameterGroup />
    <Task>
      <Reference Include="System.Xml"/>
      <Using Namespace="System"/>
      <Using Namespace="System.IO"/>
      <Using Namespace="System.Reflection"/>
      <Using Namespace="System.Xml"/>
      <Using Namespace="System.Security.Cryptography"/>
      <Code Type="Fragment" Language="cs">
<![CDATA[
var fileName = ".\\Web.Config";
var xmlDoc = new XmlDocument();
xmlDoc.Load(fileName);

var configurationNode = xmlDoc.SelectSingleNode("/configuration");
if (configurationNode == null)
{
  Log.LogMessage(
    "Cannot find configuration - Create it...", 
    MessageImportance.High);
  configurationNode = xmlDoc.CreateElement("configuration");
  //xmlDoc.DocumentElement.AppendChild(configurationNode);
}

var systemWebNode = xmlDoc.SelectSingleNode("/configuration/system.web");
if (systemWebNode == null)
{
  Log.LogMessage(
    "Cannot find system.web - Create it...", 
    MessageImportance.High);
  systemWebNode = xmlDoc.CreateElement("system.web");
  configurationNode.AppendChild(systemWebNode);
}

var machineKeyNode = 
  xmlDoc.SelectSingleNode("/configuration/system.web/machineKey")
    as XmlElement;
if (machineKeyNode == null)
{
  Log.LogMessage(
    "Cannot find machineKey - Create it...", 
    MessageImportance.High);
  machineKeyNode = xmlDoc.CreateElement("machineKey");
  systemWebNode.AppendChild(machineKeyNode);
}

machineKeyNode.Attributes.RemoveAll();

machineKeyNode.SetAttribute(
  "validation", 
  "HMACSHA512");

machineKeyNode.SetAttribute(
  "decryption", 
  "AES");

var rng = new RNGCryptoServiceProvider();

var validationKey = new byte[64];
rng.GetBytes(validationKey);

machineKeyNode.SetAttribute(
  "validationKey", 
  string.Join("", validationKey.Select(x => x.ToString("x2"))));

var decryptionKey = new byte[16];
rng.GetBytes(decryptionKey);

machineKeyNode.SetAttribute(
  "decryptionKey", 
  string.Join("", decryptionKey.Select(x => x.ToString("x2"))));

Log.LogMessage(
  "Updated decryption key and validation key of machineKey section", 
  MessageImportance.High);

xmlDoc.Save(fileName);
]]>
      </Code>
    </Task>
  </UsingTask>


  <Target Name="GenerateMachineKeyPreTransformWebConfig" BeforeTargets="PreTransformWebConfig">
    <Message Text="GenerateMachineKeyPreTransformWebConfig" Importance="High" />
    <GenerateMachineKey Condition="'$(Configuration)' == 'Release'" />
  </Target>

</Project>