WP Weixin - Force users to be followers even if they are not using the WeChat built-in browser.

wp-weixin-force-follow-all-browsers.php

<?php
// Place this code in your child theme's functions.php or in one of your custom plugins
// Adds an action before displaying a page
add_action( 'template_redirect', 'wp_weixin_force_follow_all_browsers', 0, 0 );

// The action executed before displaying a page
function wp_weixin_force_follow_all_browsers() {
	// change `home_url( '/' )` with the URL of an existing page with your Official Account QR code of your choice,
	// or add a WordPress filter "wp_weixin_force_follow_all_browsers_url" of your own to change the destination
	$page_url = apply_filters( 'wp_weixin_force_follow_all_browsers_url', home_url( '/' ) );

	// get the current URL
	if (
		isset( $_SERVER['HTTPS'] ) &&
		( 'on' === $_SERVER['HTTPS'] || 1 === intval( $_SERVER['HTTPS'] ) ) ||
		isset( $_SERVER['HTTP_X_FORWARDED_PROTO'] ) &&
		'https' === $_SERVER['HTTP_X_FORWARDED_PROTO']
	) {
		$protocol = 'https://';
	} else {
		$protocol = 'http://';
	}

	$current_url = $protocol . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] . $_SERVER['QUERY_STRING'];

	if ( ! empty( $_SERVER['QUERY_STRING'] ) ) {
		$current_url .= '?' . $_SERVER['QUERY_STRING'];
	}

	// get the current user
	$user = wp_get_current_user();

	if (
		// check the page is NOT the page with your Official Account QR code
		$current_url !== $page_url &&
		// check WP Weixin is activated
		function_exists( 'wp_weixin_is_wechat' ) &&
		// check we're not in the admin backend
		! is_admin() &&
		(
			// check:
			// - if the user is not logged in OR
			// 	- if the browser is not wechat built-in AND
			// 	- the current user is not a follower
			! is_user_logged_in() ||
			(
				! wp_weixin_is_wechat() &&
				! wp_weixin_is_follower( $user->ID )
			)
		)
	) {
		// redirect to the page with your Official Account QR code
		wp_safe_redirect( $page_url );

		// stop execution, we're done!
		exit();
	}
}