I have written several integrations (eg. for Vanilla forum and Mediawiki) using the Elgg cookie.

You just need to write a bit of code allowing each app to access the other's database tables and you're up and running.

Thanks, Kevin;

can you name the steps to do the external app->elgg automatic login?  I gess that you send a login HTML request with the user name as param and then override the Elgg auth system to read the user / key pair in the external database...

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salva

I suggest that you look at the source for one of the plugins I mentioned.

I don't over-ride the Elgg auth system. Elgg is the auth system. I over-ride the other app's system to authenticate off the Elgg cookie.

So in that sense, Elgg is the master and the other app is the slave.

Having said that, it is easy enough to do it the other way round.

the structure would be:

$username = get_username_from_other_app_cookie();

$user = get_user_by_username($username);

login($user);

Ok, but where would you put that code? It doesn't seem to work doing that into engine/lib/sessions.php->authenticate

You would put it in a plugin.

Never alter core code.