I am using https://github.com/google/google-api-php-client to get acccess token. and i am getting following error.
PHP
Fatal error: Uncaught exception 'LogicException' with message 'config parameter "signing_key" must be set to refresh a token with assertion' in /Users/CFADMIN/Work/googleanalytics/google-api-php-client/src/Google/Client.php:201
can anyone tell what is signing key. and how can i resolve this problem?