Allow CORS for WP API - Along with sending Status 200 for OPTIONS request

functions.php

add_action( 'init', 'handle_preflight' );

function handle_preflight() {
	
	$origin = get_http_origin();

 	if ( $origin == 'http://localhost:8080' ||	$origin == 'https://yourapp.firebaseapp.com') {
		
    header("Access-Control-Allow-Origin: " . $origin);
		header("Access-Control-Allow-Methods: POST, GET, OPTIONS, PUT, DELETE");
		header("Access-Control-Allow-Credentials: true");
		header( 'Access-Control-Allow-Headers: Authorization' );

		if ( 'OPTIONS' == $_SERVER['REQUEST_METHOD'] ) {
			status_header(200);
			exit();
		}
	}
}