default: /piwik/ - you can chance that to whatever you want/need
PIWIK_NOT_BEHIND_PROXY
default: not set - if set to any value the settings to listen behind a reverse proxy server will be removed
PIWIK_PROXY_HEADER
default: HTTP_X_FORWARDED_FOR - if set Piwik will attempt to use the given header to determine the original client address.
HTTP_CF_CONNECTING_IP or HTTP_CLIENT_IP may be helpful if behind certain proxies.
PIWIK_HSTS_HEADERS_ENABLE
default: not set - if set to any value the HTTP Strict Transport Security will be activated on SSL Channel
PIWIK_HSTS_HEADERS_ENABLE_NO_SUBDOMAINS
default: not set - if set together with PIWIK_HSTS_HEADERS_ENABLE and set to any value the HTTP Strict Transport Security will be deactivated on subdomains
PIWIK_PLUGINS_ACTIVATE
default: not set - if set Piwik will activate the Plugins named in the Variable, separated by whitespace