The people managing the 15.wikipedia.org site needs access to https://piwik.wikimedia.org/ for analytics reporting. Their user names are:
I'm not 100% sure they have labs accounts, I'll check with them.
Piwik uses labs ldap as can be seen here:
https://github.com/wikimedia/operations-puppet/blob/088fe6a3f7198acba1e2a82817a3fae033f42d9c/manifests/role/piwik.pp#L47