Function hkdf_expand_label 

pub fn hkdf_expand_label(
    provider: &impl CryptoProvider,
    suite: CipherSuite,
    secret: &Hash,
    label: &[u8],
    context: &[u8],
    out: &mut [u8],
) -> Result<(), Error>

HKDF-Expand-Label as defined in RFC 8446 §7.1.

Derives keying material from a secret using a labeled context. out must be sized to the desired output length.