Voluntary Aadhaar authentication: entities must meet privacy standards and cannot deny services for refusal, except where law mandates. The amendment makes Aadhaar use for identity voluntary with informed consent for authentication or offline verification; allows entities to perform authentication only if they meet regulatory privacy and security standards and are authorised by law or prescribed by the Central Government; permits the Authority to require use of actual Aadhaar numbers or a virtual identity; requires requesting entities to offer alternate identification and not to deny services for refusal; and permits mandatory authentication where a parliamentary law requires it.