Pass props through CreateAppContainer

You have to scope the props under screenProps to be able to access it at the screen level.

// App.js
<AppNavigator
  screenProps={{
    handler: () => {},
    hello: "World"
  }}
/>

// Navigator.js
const StackNavigator = createStackNavigator({
  Login: {
    screen: ({ screenProps, navigation }) => {
      screenProps.handler();

      // ...
    },
  },
})

Okay, I got this to work with help of Samuel Vaillant. I had to make couple of modifications.

My App.js:

render() {
        return (
            this.state.isLoggedIn ? <DrawerNavigator /> : <SignedOutNavigator
                screenProps={{
                    handler: (settings) => { this.saveUserSettings(settings) }
                }}
            />
        )
    }

My SignedOutNavigator:

import React from "react";
import { View, Text } from "react-native";
import { createStackNavigator, createAppContainer } from "react-navigation";
import LoginScreen from "../screens/LoginScreen";

const SignedOutNavigator = createStackNavigator({
    Login: {
        // screen: LoginScreen
        screen: screenProps => <LoginScreen screenProps={value => {
            screenProps.screenProps.handler(value)
        }} />,
        navigationOptions: ({ navigation }) => ({
            header: null,
        }),
    }
});

export default createAppContainer(SignedOutNavigator);