How can i change the login flow

hi guys im new to nextcloud. i want to change the nextcloud login flow I have and app where i want nextcloud to be integrated, integrations comes next first i need to change the login flow for my nexcloud instance, i dont want to open frame and let users login nextcloud and authenticate the app from there.

i want users login from my app. i dont want to implement SSO. is there any other way that i can tweak to get my users login to nextcloud when they login to my app, without opening a frame for users to authenticate from nextcloud.

i dont want users to login to my app and then to nextcloud again thats a lengthy process. i want to login users from my app directly to nextcloud without using sso or Iframe.

OR

I there any way to access my nextcloud custom extension/app api for authorization and login to nextcoud, currently i cant access my app/extension without login from nextcloud.