Function that implements HMAC SHA-256 encryption algorithm

Hi

I need MQL4 function that computes a Hash-based Message Authentication Code (HMAC) by using the SHA256 hash function.

HMAC encryption algorithm similar to 

https://msdn.microsoft.com/en-us/library/system.security.cryptography.hmacsha256(v=vs.110).aspx

https://en.wikipedia.org/wiki/Hash-based_message_authentication_code 

MQL has all necessary functions for this and I've started the code but need someone to finish it.

The code must use only MQL language, no external C libraries.

 Using methods like: 

   res=CryptEncode(CRYPT_HASH_SHA256,src,key,dst32);

   res=CryptEncode(CRYPT_BASE64,dst32,empty,dst);

Cheers

John.