Build a StoredToken from a freshly issued TokenSet, computing the
absolute expiry from now + expiresIn (only when expiresIn is
positive). A TokenSet from a refresh that omits refresh_token keeps
prevRefresh (RFC 6749 allows the AS to reissue or retain it).
Build a StoredToken from a freshly issued TokenSet, computing the absolute expiry from now + expiresIn (only when expiresIn is positive). A TokenSet from a refresh that omits refresh_token keeps prevRefresh (RFC 6749 allows the AS to reissue or retain it).