React Native Custom Login without Password Grant

I am trying to implement custom login flow and want to avoid web based login flow for some reason.
I have tried “react-native-auth0” package for this purpose.
But to achieve email/password login I had to enable Password Grant so that I can use “auth0.auth.passwordRealm()”

Is there any way to achieve same without enabling password grant?
for web based app using Auth0-js library you don’t need to do this, why this inconsistency among these sdk?