ccess an online service, users need to authenticate to
the service&mdash;they need to provide proof of their identity. For an
application that accesses a third-party service, the security problem is even
more complicated. Not only does the user need to be authenticated to access the
service, but the application also needs to be authorized to act on the user's
behalf. </p>

<p>The industry standard way to deal with authentication to third-party services
is the OAuth2 protocol. OAuth2 provides a single value,