Cargo Features

[dependencies]
hawk = { version = "5.0.1", default-features = false, features = ["use_ring", "use_openssl"] }
default = use_ring

The use_ring feature is set by default whenever hawk is added without default-features = false somewhere in the dependency tree.

use_ring default = ring
use_openssl = openssl

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

ring use_ring
openssl use_openssl?