I use google-api-php-client library to access webmaster tools data. When I wanted to list sitemaps, it appeared Fatal error: Uncaught exception 'Google_Service_Exception'(403) User does not have sufficient permission for site. See also: https://support.google.com/webmasters/answer/2451999.' I add the service account email address as a restrict user for my site, but error still exists.
Finally I find the answer: A service account is not like a regular Google account. You cannot use it to access specific resources even if you give that specific address "access" to it. See here for the different ways you can authorize your requests to the Webmaster API.