Prevent direct access via URL to a WordPress page

functions.php

<?php 
function prefix_no_direct_access() {
	// Define Page URL for redirect.
	$careers = get_permalink( get_page_by_title( 'Careers' ) );
	
	// If this is not the Apply Now page, do nothing.
	if( ! is_page( 'Apply Now' ) ) {
		return;
	}

	// Allow direct access to logged in users who can edit pages.
	if( is_user_logged_in() && current_user_can( 'edit_posts' ) ) {
		return;
	}
	
	// Get the referrer from the server request.
	$referer = wp_get_referer();

	// If we have a referer...
	if( isset( $referer ) ) {
		// Parse the URL.
		$refer_URL = parse_URL( $referer );
		// Check for Position in the referrer path.
		$position = strpos( $refer_URL[ 'path' ], 'position' );
		// Verify the referer is from our site. Because, referer spoofing.
		$validate_position = url_to_postid( $referer );
		// If `position` is in referer path and it is from our site, do nothing. Referer is valid.
		if( $position > -1 && $validate_position > 0 ) {
			return;
		} else { // Referer invalid, redirect.
			nocache_headers();
			wp_safe_redirect( $careers );
			exit;
		}
	// Otherwise no referer, redirect.
	} else {
		nocache_headers();
		wp_safe_redirect( $careers );
		exit;
	}
}
add_action( 'template_redirect', 'prefix_no_direct_access' );