External login/autolog in NextCloud 12

Hello everybody!

I have a system currently (in which I previously have to log in). Once I login, I have a sidebar with different applications. One of them has to be a link to NextCloud, so if the user clicks on that link, it will send to Nextcloud a token with the user and session ID, so I want to show its own NextCloud dock without needing to require authentication (again).

It could be possible? Is there is any manual?