This has nothing to do with tooling or with implementation details. If it did then we'd be talking about SAML tokens or doing the OAuth dance. What you're describing above as 'implementation details' is actually a system behaviour. Description of system behaviours is what is commonly known as a Functional Specification. We call a specific system behaviour a Feature. A set of Features is our Specification. Note that I haven't used the term 'user story' anywhere in this paragraph.
This article is all about communicating using well-defined and tightly-scoped terms, i.e. not user stories. It's also about bridging the gap between requirements and specifications using impact mapping.
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