Function verify_key 

async fn verify_key(
    session_key: &[u8],
    username: &str,
    key_uuid: &str,
    salt: &[u8],
    shared_a: &BoxedUint,
    shared_b: &BoxedUint,
    rest: &RestClient,
) -> Result<(), OnePasswordError>

Sends the client verification hash to confirm the session key, then checks the server’s answer.