Disable password field from encrpyting value

I follow this tutorial and created my own field--License. It is a password input but saves as normal text in the admin.

https://docs.metabox.io/custom-field-type/

if ( class_exists( 'RWMB_Field' ) ) {
        /**
     * Metabox Field
     * 
     * Create new field to store access token in admin.
     *<br />
     * Obfuscates the view to the end user but saves as plain text in the database.
     * 
     * @since 5.1.0
     */
    class RWMB_License_Field extends RWMB_Field {
        /**
         * Render the field
         *
         * @param string $meta Value from input.
         * @param array $field Field data.
         * @return string
         * @since 5.1.0
         */
        public static function html( $meta, $field ) {
            return sprintf(
                '<input type="password" name="%s" id="%s" value="%s" size="%s">',
                $field['field_name'],
                $field['id'],
        $meta,
        $field['size']
            );
        }
    }
}