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.

[dependencies]
actix-web = { version = "4", features = ["openssl"] }
openssl = { version = "0.10", features = ["v110"] }

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.