ALPN stands for Application-Layer Protocol Negotiation. It’s a Transport Layer Security (TLS) extension that aids client and server identification during secure data transfers. ALPN is an automated standard for how servers talk to each other — ALPN works in the early stages of a TLS handshake to help parties immediately identify each other and agree on protocols to avoid backtracking later.
ALPN is more secure and efficient than older negotiation methods, like lower-security Next Protocol Negotiation. It also optimizes updated protocols such as HTTP/2, which aids load time and encryption more than HTTP/1 can.