[pmwiki-users] Have a canonical url declaration : how to ?

[ABClf]

Hello hello,

I'm playing with google search console ; there I see I am missing a
canonical url.

Most of my pages are visible at these different url :
http://www.mysite.com/Group/Name
http://www.mysite.com/Group.Name
http://www.mysite/com/pub/htmlcache/Group.Name.html

I believe I need a link rel=canonical somewhere to make different url
point to a unique url (avoiding duplicate content) ;
what would be the strategy to get it done ? (note : in my special
case, most of the pages are saved in cache using fastcache recipe to
be served quickly on request).
Do I have to write something in template, using Name and Group ? or
would a dedicated script in config do better job ?

(by the way, perhaps might be good to have such canonical thing if
"action" pages).

Thank you,
Gilles.