actix-web automatically upgrades connections to HTTP/2 if possible.

Negotiation

When either of the rustls or openssl features are enabled, HttpServer provides the bind_rustls() method and bind_openssl() methods, respectively.

Upgrades to HTTP/2 described in RFC 7540 §3.2 are not supported. Starting HTTP/2 with prior knowledge is supported for both cleartext and TLS connections (RFC 7540 §3.4) (when using the lower level actix-http service builders).

Check out the TLS examples for concrete example.