Client Credentials Flow
Problem
- Your Orders, Billing, and Reporting services all call your Inventory service using one shared static API key.
- The Reporting service is retired, but its copy of the key still works.
- Turning that key off would also cut off Orders and Billing, since they use the exact same one.
A secret shared by every caller can only ever be revoked for every caller at once.
Solution
Client Credentials Flow
- Register each service as its own identity in Microsoft Entra ID.
- Before calling Inventory, a service requests its own short-lived token using its own credentials.
- Inventory checks that token on every call, so it can tell exactly who's calling, and revoke just one.
Give every caller its own identity, and you can always cut off one without touching the rest. That per-service token exchange is the client credentials flow.
Analogy
A warehouse could hand every delivery driver a copy of the same master keycard.
Instead, each driver gets their own badge, tied to their own name. When one driver leaves the company, security switches off that one badge, and every other driver keeps working exactly as before.
The client credentials flow is each service getting its own badge, instead of sharing one master key with everyone else.
