Check User Password complex validation

gistfile1.cs

namespace Sitecore.Form.Submit
{
	public class CheckUserPassword : CheckUserAction
	{
	...
		public override void Execute(ID formid, IEnumerable<ControlResult> fields)
		{
			string empty;
			string failedMessage = base.FailedMessage;
			string str = failedMessage;
			if (failedMessage == null)
			{
				str = ResourceManager.GetString("USER_NAME_OR_PASSWORD_IS_INCORRECT");
			}
			string str1 = str;
			
			ControlResult controlResult = fields.FirstOrDefault<ControlResult>((ControlResult f) => f.FieldID == base.UserNameField);
			ControlResult controlResult1 = fields.FirstOrDefault<ControlResult>((ControlResult f) => f.FieldID == this.PasswordField);
			if (controlResult != null)
			{
      			...