Derives a credential several processes of this service must arrive at independently: an HMAC-SHA-256 of the label and parts under a shared secret.
the shared secret
what the credential is for, so one purpose's credential is never another's
further inputs, each separated by a NUL
the credential, base64url
Derives a credential several processes of this service must arrive at independently: an HMAC-SHA-256 of the label and parts under a shared secret.