How to access/modify customer login logic on shopify

We are looking to modify the login flow from email + password to a phone number + otp based login flow

We already have our own otp based service we can utilise

On looking through the theme code, i cannot find any files which contain the logic that controls how a new user is created / how a user is verified and logged in ( i have seen login.liquid and register.liquid which i have used to add input boxes to accept phone numbers )

Outside of using external applications, if we were to create a custom page to login users, how would i access shopify customer information? (store new users, verify + login new users etc)

I have sent you an email from my work mail ID ending in nativehealth.in

@NativeHealth_R , Hope you are doing well.

You can use he Shopify app to use OTP-based functionality for the login. There are some apps available on the store.