How to generate a checksum file using HMAC SHA 256 algorithm?

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C#

ASP.NET

I am generating checksum file using SHA 256 Algorithm. But I need to update using HMAC SHA 256 Algorithm.

What I have tried:

Currently we are doing the same using SHA 256 AS BELOW:

public string GetChecksum(string strValue)
      {
          string strSHA256TOString = string.Empty;
          //Modified to windows - 1256 29-04-2012
          //byte[] bBytes = Encoding.UTF8.GetBytes(strValue);
          byte[] bBytes = Encoding.GetEncoding("windows-1256").GetBytes(strValue);
          var sha = new SHA256Managed();

          byte[] bChecksum = sha.ComputeHash(bBytes);
          strSHA256TOString = BitConverter.ToString(bChecksum).Replace("-", String.Empty);
          return strSHA256TOString.ToLower();
      }