code: def hmac_hex_key(self, hmac_hex_key):
          
          if hmac_hex_key is None:
              raise ValueError("Invalid value for `hmac_hex_key`, must not be `None`")
          if hmac_hex_key is not None and len(hmac_hex_key) > 64:
              raise ValueError("Invalid value for `hmac_hex_key`, length must be less than or equal to `64`")
          if hmac_hex_key is not None and not re.search('^([a-fA-F0-9][a-fA-F0-9]){1,32}$', hmac_hex_key):
              raise ValueError("Invalid value for `hmac_hex_key`, must be a follow pattern or equal to `/^([a-fA-F0-9][a-fA-F0-9]){1,32}$/`")
  
          self._hmac_hex_key = hmac_hex_key
docs: Sets the hmac_hex_key of this CfsslAuthCredentials.
          The key that is used to compute the HMAC of the request using the HMAC-SHA-256 algorithm. Must contain an even number of hexadecimal characters. 
  
          :param hmac_hex_key: The hmac_hex_key of this CfsslAuthCredentials.
          :type: str