Thanks for the very very quick response 
Hmm okay, well I found a setting in the discourse settings section. This allows the forum to be iframed into another site. This setting works (if you are already logged in and have the cookie).
The only thing which doesn’t work is the sso process. Our sso process works fine and correct when opening the forum in a new tab. But the iframe breaks this process because the cookie with the accesstoken cannot be set due to a different domain. This leads to an endless loop inside of the iframe because discourse can’t find this cookie and starts the sso process again.
As this is very important for us, isn’t there any option to iframe the forum whilst using sso authentication?