Hello @mennobouma ,
Safari is a very strict browser.
The issue doesn’t come from the plugin, but from the fact that Safari considers all cross-domain cookies as “tracking”, and blocks them by default. It is true this is the same technology Facebook and other intrusive services use, but “tracking” (which is somehow a loaded word in that context) is sometimes what the users need or want.
The only reliable way to enable cross-domain login and logout in Safari browser for now is to have the users allow it in their browser preference (Safari > Preferences > Privacy > Website tracking > untick “Prevent cross-site tracking”).
I am aware it is less than ideal. I wish there was a workaround. Looking around the web, the issue is at least 11 years old, and past workarounds have been relentlessly and quickly patched by Apple.
Moving forward, I can see something like a modal window displayed at login & logout in Safari only, in which one-time-clickable links would invite the user to take action. These links would explicitly go to the remote site in a new tab that would immediately close after setting the cookies.
There may be other solutions possible, but all of them would require explicit user interaction. More information can be found in this announcement on webkit.org.
I find these alternatives way less elegant than under-the-hood login/logout, and I still need to wrap my head around how to actually code it, in the event I go through with it.