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Requesting New Assertions vs Existing Assertions
•Sometimes an IdP will create a new assertion when invoked by a request from a SP.
–Example: if a SP issues an AuthnRequest with ForceAuthn="true" then the IdP must create a new assertion (he cannot simply return an existing assertion).
•Sometimes a SP simply wants an existing assertion. 
•The following slides show the ways a SP can issue a request for an existing assertion.