Next Cloud User Management implementation in WebApp

I have developed a next cloud application. I want to implement following :

Sign up and register on nextcloud application. I do not want user to access the next cloud login… I want when user lands up on website , he get to see Login page from Application not from next cloud.

I do not want to access the FOLDERS and FILES of next cloud. The user who login will only have an access to next cloud application.

Please advise.