def authenticate(self, login=None, password=None):
        '''
        Authenticated this client instance.

        ``login`` and ``password`` default to the environment
        variables ``MS_LOGIN`` and ``MS_PASSWD`` respectively.


        :param login: Email address associated with a microsoft account
        :param password: Matching password

        :raises: :class:`~xbox.exceptions.AuthenticationException`

        :returns: Instance of :class:`~xbox.Client`

        '''
        if login is None:
            login = os.environ.get('MS_LOGIN')

        if password is None:
            password = os.environ.get('MS_PASSWD')

        if not login or not password:
            msg = (
                'Authentication credentials required. Please refer to '
                'http://xbox.readthedocs.org/en/latest/authentication.html'
            )
            raise AuthenticationException(msg)

        self.login = login

        # firstly we have to GET the login page and extract
        # certain data we need to include in our POST request.
        # sadly the data is locked away in some javascript code
        base_url = 'https://login.live.com/oauth20_authorize.srf?'

        # if the query string is percent-encoded the server
        # complains that client_id is missing
        qs = unquote(urlencode({
            'client_id': '0000000048093EE3',
            'redirect_uri': 'https://login.live.com/oauth20_desktop.srf',
            'response_type': 'token',
            'display': 'touch',
            'scope': 'service::user.auth.xboxlive.com::MBI_SSL',
            'locale': 'en',
        }))
        resp = self.session.get(base_url + qs)

        # python 3.x will error if this string is not a
        # bytes-like object
        url_re = b'urlPost:\\\'([A-Za-z0-9:\?_\-\.&/=]+)'
        ppft_re = b'sFTTag:\\\'.*value="(.*)"/>'

        login_post_url = re.search(url_re, resp.content).group(1)
        post_data = {
            'login': login,
            'passwd': password,
            'PPFT': re.search(ppft_re, resp.content).groups(1)[0],
            'PPSX': 'Passpor',
            'SI': 'Sign in',
            'type': '11',
            'NewUser': '1',
            'LoginOptions': '1',
            'i3': '36728',
            'm1': '768',
            'm2': '1184',
            'm3': '0',
            'i12': '1',
            'i17': '0',
            'i18': '__Login_Host|1',
        }

        resp = self.session.post(
            login_post_url, data=post_data, allow_redirects=False,
        )

        if 'Location' not in resp.headers:
            # we can only assume the login failed
            msg = 'Could not log in with supplied credentials'
            raise AuthenticationException(msg)

        # the access token is included in fragment of the location header
        location = resp.headers['Location']
        parsed = urlparse(location)
        fragment = parse_qs(parsed.fragment)
        access_token = fragment['access_token'][0]

        url = 'https://user.auth.xboxlive.com/user/authenticate'
        resp = self.session.post(url, data=json.dumps({
            "RelyingParty": "http://auth.xboxlive.com",
            "TokenType": "JWT",
            "Properties": {
                "AuthMethod": "RPS",
                "SiteName": "user.auth.xboxlive.com",
                "RpsTicket": access_token,
            }
        }), headers={'Content-Type': 'application/json'})

        json_data = resp.json()
        user_token = json_data['Token']
        uhs = json_data['DisplayClaims']['xui'][0]['uhs']

        url = 'https://xsts.auth.xboxlive.com/xsts/authorize'
        resp = self.session.post(url, data=json.dumps({
            "RelyingParty": "http://xboxlive.com",
            "TokenType": "JWT",
            "Properties": {
                "UserTokens": [user_token],
                "SandboxId": "RETAIL",
            }
        }), headers={'Content-Type': 'application/json'})

        response = resp.json()
        self.AUTHORIZATION_HEADER = 'XBL3.0 x=%s;%s' % (uhs, response['Token'])
        self.user_xid = response['DisplayClaims']['xui'][0]['xid']
        self.authenticated = True
        return self
Authenticated this client instance.

        ``login`` and ``password`` default to the environment
        variables ``MS_LOGIN`` and ``MS_PASSWD`` respectively.


        :param login: Email address associated with a microsoft account
        :param password: Matching password

        :raises: :class:`~xbox.exceptions.AuthenticationException`

        :returns: Instance of :class:`~xbox.Client`