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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def authenticate(self, username, password, service='login', encoding='utf-8', resetcreds=True):
 """username and password authentication for the given service. Returns True for success, or False for failure. self.code (integer) and self.reason (string) are always stored and may be referenced for the reason why authentication failed. 0/'Success' will be stored for success. Python3 expects bytes() for ctypes inputs. This function will make necessary conversions using the supplied encoding. Inputs: username: username to authenticate password: password in plain text service: PAM service to authenticate against, defaults to 'login' Returns: success: True failure: False """


        @conv_func
        def my_conv(n_messages, messages, p_response, app_data):
            """Simple conversation function that responds to any
               prompt where the echo is off with the supplied password"""
            # Create an array of n_messages response objects
            addr = calloc(n_messages, sizeof(PamResponse))
            response = cast(addr, POINTER(PamResponse))
            p_response[0] = response
            for i in range(n_messages):
                if messages[i].contents.msg_style == PAM_PROMPT_ECHO_OFF:
                    dst = calloc(len(password)+1, sizeof(c_char))
                    memmove(dst, cpassword, len(password))
                    response[i].resp = dst
                    response[i].resp_retcode = 0
            return 0

        # python3 ctypes prefers bytes
        if sys.version_info >= (3,):
            if isinstance(username, str): username = username.encode(encoding)
            if isinstance(password, str): password = password.encode(encoding)
            if isinstance(service, str):  service  = service.encode(encoding)
        else:
            if isinstance(username, unicode):
                username = username.encode(encoding)
            if isinstance(password, unicode):
                password = password.encode(encoding)
            if isinstance(service, unicode):
                service  = service.encode(encoding)

        if b'\x00' in username or b'\x00' in password or b'\x00' in service:
            self.code = 4  # PAM_SYSTEM_ERR in Linux-PAM
            self.reason = 'strings may not contain NUL'
            return False

        # do this up front so we can safely throw an exception if there's
        # anything wrong with it
        cpassword = c_char_p(password)

        handle = PamHandle()
        conv   = PamConv(my_conv, 0)
        retval = pam_start(service, username, byref(conv), byref(handle))

        if retval != 0:
            # This is not an authentication error, something has gone wrong starting up PAM
            self.code   = retval
            self.reason = "pam_start() failed"
            return False

        retval = pam_authenticate(handle, 0)
        auth_success = retval == 0

        if auth_success and resetcreds:
            retval = pam_setcred(handle, PAM_REINITIALIZE_CRED);

        # store information to inform the caller why we failed
        self.code   = retval
        self.reason = pam_strerror(handle, retval)
        if sys.version_info >= (3,):
            self.reason = self.reason.decode(encoding)

        if hasattr(libpam, 'pam_end'):
            pam_end(handle, retval)

        return auth_success