Was React Native a bad decision, ugly authentication has me ready to switch

I found that to authenticate using Javascript Server, it requires using implicit grants on the API.

This looks uncomfortably cheap, with the web browser opening to authenticate.

I dont think I can have something that looks so primitive for my app, even if it is additional security.

Considering doing full development for Web, android, and iphone. I already have my back end done.

React Native doesnt seem useful if I need to authenticate using web. Any ideas before I buy my first apple product ever and go full iOS?