Answer
Not by using the external identity provider's token directly — IFS Cloud's IAM only accepts access tokens it issued itself, and swapping an external token for an IFS-issued one ("token exchange") is disabled by default and isn't something available to reconfigure in a standard SaaS setup; the supported pattern instead is to have the application's login flow go through IFS IAM itself (using the standard Authorization Code flow with PKCE), with IAM brokering the actual sign-in to your external identity provider behind the scenes — that way the token your app ends up with is always an IFS-IAM-issued one carrying the real end user's identity and permissions.