code: def sign_sha256(key, msg):
          
          if isinstance(msg, text_type):
              msg = msg.encode('utf-8')
          return hmac.new(key, msg, hashlib.sha256).digest()
docs: Generate an SHA256 HMAC, encoding msg to UTF-8 if not
          already encoded.
  
          key -- signing key. bytes.
          msg -- message to sign. unicode or bytes.