answers.sap.com/questions/12294558/hmac-sha256-result-sap-vs-java.html

you can calculate HMAC-256. I did it for key = "ABC" and data = "ABC". The result is 87bed3bb8821d3196854b37290e5a1c3e518f99eff4101219d1d492fed1eba1a. To get the same value you have to first convert ABC to xstring using method STRING_TO_XSTRING. This gives you 414243. Then if you just set key to 414243 and data to ABC then the returned MAC from CALCULATE_HMAC_FOR_CHAR is same as the one above. I did this all in SE24 just by testing the class.