public static void Main()
var _requestData = "username=test01&password=aaaaaa&otp=123456&__RequestVerificationToken";
var startIndex = _requestData.IndexOf("password=");
var endIndex = _requestData.IndexOf("otp=");
if (endIndex > -1 && endIndex > startIndex)
Console.WriteLine(startIndex);
Console.WriteLine(endIndex);
startIndex = startIndex + "password=".Length;
_requestData = _requestData.Remove(startIndex, endIndex - startIndex);
_requestData = _requestData.Insert(startIndex, "********");
Console.WriteLine(_requestData);