diff --git a/.changeset/pink-geese-teach.md b/.changeset/pink-geese-teach.md
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+---
+'@backstage/backend-defaults': minor
+'@backstage/backend-test-utils': minor
+---
+
+Added `actor` property to `BackstageUserPrincipal` containing the subject of the last service (if any) who performed authentication on behalf of the user.