Manual:$wgCanonicalServer

Details
Server name with protocol (HTTP or HTTPS) to use for links to the wiki from IRC feeds and e-mail notifications. Must be fully qualified, even if $wgServer is protocol-relative.

You can often ignore this variable. However, if you have set $wgServer to a protocol-relative URL (for example, ) and you would like links to your wiki to use HTTPS, set this variable to the equivalent HTTPS URL (for example,  ).