Macro const_hasher 

macro_rules! const_hasher {
    ($m_name: ident, $key_name: literal) => { ... };
}

key should be Base64Url decoded 56 bytes long (~ 75 chars)

const_hasher!(module_name, "ENV_KEY_NAME");

env key concatenated with “APP_ID_KEY_” will be used to get the key