Gets temporary S3 credentials to stage user-uploaded files

def _get_credentials(self):
        """Gets temporary S3 credentials to stage user-uploaded files
        """
        uri = URITemplate(self.baseuri + '/{username}/credentials').expand(
            username=self.username)

        resp = self.session.post(uri)

        self.handle_http_error(
            resp,
            custom_messages={
                401: "Token is not authorized",
                404: "Token does not have upload scope",
                429: "Too many requests"})
        return resp