If API consumers not only call API, but also access private
data, then API key is not good enough to authenticate API
users, the OAuth clientID can be for protecting this type of
API access [9].
OpenID (OID) is an open authentication standard and
decentralized protocol [21] that allows users to be
authenticated by certain co-operating web sites using a third
party service. With OID, users can log into multiple different
web sites owned by different companies in Replying Parties
group without registering with their information for each web
site. OpenID Connect is the latest OpenID standard, which
integrates OAuth2 as its authorization protocol.