Shortcut for requests.request with proper Authorization header.

        Note:
            If you put auth keyword argument or Authorization in headers
            keyword argument, this will raise an exception.
            Decide what you want to do!

        Args:
            method (str) - HTTP method of this request, like GET or POST.
            url (str) - URL of this request (one of Google APIs).

        Examples:
            >>> scope = 'https://www.googleapis.com/auth/plus.login'
            >>> url = 'https://www.googleapis.com/plus/v1/people' \
            >>>         '?query=Guuido+van+Rossum'
            >>> key = json.load(open('/path/to/credentials.json'))
            >>> auth = ServiceAccount.from_json(key=key, scopes=scope)
            >>> auth.authorized_request(method='get', url=url)

        Returns:
            requests.Response

def authorized_request(self, method, url, **kwargs):
        """Shortcut for requests.request with proper Authorization header.

        Note:
            If you put auth keyword argument or Authorization in headers
            keyword argument, this will raise an exception.
            Decide what you want to do!

        Args:
            method (str) - HTTP method of this request, like GET or POST.
            url (str) - URL of this request (one of Google APIs).

        Examples:
            >>> scope = 'https://www.googleapis.com/auth/plus.login'
            >>> url = 'https://www.googleapis.com/plus/v1/people' \
            >>>         '?query=Guuido+van+Rossum'
            >>> key = json.load(open('/path/to/credentials.json'))
            >>> auth = ServiceAccount.from_json(key=key, scopes=scope)
            >>> auth.authorized_request(method='get', url=url)

        Returns:
            requests.Response
        """
        headers = kwargs.pop('headers', {})
        if headers.get('Authorization') or kwargs.get('auth'):
            raise ValueError("Found custom Authorization header, "
                             "method call would override it.")
        headers['Authorization'] = 'Bearer ' + self.access_token

        return requests.request(method, url, headers=headers, **kwargs)