<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _security_auth_headers(self, username, password, headers):
 """ Add in the requisite HTTP Authentication Headers :param username: Riak Security Username :type str :param password: Riak Security Password :type str :param headers: Dictionary of headers :type dict """

        userColonPassword = username + ":" + password
        b64UserColonPassword = base64. \
            b64encode(str_to_bytes(userColonPassword)).decode("ascii")
        headers['Authorization'] = 'Basic %s' % b64UserColonPassword