Get an access token from an username and password combination.
        In order to get this working you need to create an app at
        http://twitter.com/apps, after that send a mail to api@twitter.com
        and request activation of xAuth for it.

def get_xauth_access_token(self, username, password):
        """
        Get an access token from an username and password combination.
        In order to get this working you need to create an app at
        http://twitter.com/apps, after that send a mail to api@twitter.com
        and request activation of xAuth for it.
        """
        try:
            url = self._get_oauth_url('access_token')
            oauth = OAuth1(self.consumer_key,
                           client_secret=self.consumer_secret)
            r = requests.post(url=url,
                              auth=oauth,
                              headers={'x_auth_mode': 'client_auth',
                                       'x_auth_username': username,
                                       'x_auth_password': password})

            credentials = parse_qs(r.content)
            return credentials.get('oauth_token')[0], credentials.get('oauth_token_secret')[0]
        except Exception as e:
            raise TweepError(e)