"Some Crypto Text";

// Compute the HMAC.
let mut ctx = MdCtx::new().unwrap();
ctx.digest_sign_init(Some(Md::sha256()), &key).unwrap();
ctx.digest_sign_update(text).unwrap();
let mut hmac = vec![];
ctx.digest_sign_final_to_vec(&mut hmac).unwrap();

// Verify the HMAC. You can't use MdCtx to do this; instead use a constant time equality check.
# let target = hmac.clone();
let valid = memcmp::eq(&hmac, &target);
assert!(valid);
```