Add hidden nonce field admin post / post type editor

admin-post-editor-nonce-field.php

<?php

/**
 * Add hidden nonce field to project post type editor.
 *
 * @param WP_Post $post Post object data.
 */
function harisrozak_add_hidden_nonce_field( $post ) {
	// Only render on a certain post type.
	if ( 'project' !== $post->post_type ) {
		return;
	}

	// Prevent the nonce field to be rendered multiple times.
	if ( defined( 'HARISROZAK_MAIN_NONCE_FIELD_RENDERED' ) ) {
		return;
	}

	define( 'HARISROZAK_MAIN_NONCE_FIELD_RENDERED', 1 );
	wp_nonce_field( 'harisrozak_admin_project_form', 'harisrozak_admin_project_form_nonce' );
}
add_action( 'edit_form_top', 'harisrozak_add_hidden_nonce_field' );

/**
 * Handles saving the meta box.
 *
 * @param int     $post_id Post ID.
 * @param WP_Post $post    Post object.
 * @return null
 */
public function harisrozak_save_metabox( $post_id, $post ) {
	$post_data = isset( $_POST ) ? wp_unslash( $_POST ) : array();
	$nonce     = isset( $post_data['harisrozak_admin_project_form_nonce'] ) ? $post_data['harisrozak_admin_project_form_nonce'] : null;

	if ( ! wp_verify_nonce( $nonce, 'harisrozak_admin_project_form' ) ) {
		return;
	}

	// The save_post data handler lies here.
}
add_action( 'save_post', 'harisrozak_save_metabox', 10, 2 );