Authentication Double-Hop is when an Authentication Method
is used by more than one Resource Server
in a series.
So Resource Owner is Authenticated or uses Delegation access to "Resource Server One".
"Resource Server One" then needs, to fulfill the request, needs to access "Resource Server Two".
Can the "Resource Server Two" determine the "Resource Server One" is performing access for the Resource Owner? This is referred to as the Confused Deputy Problem.
OAuth 2.0 Token Exchange
solves the Authentication Double-Hop issue.
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