This whitepaper introduces developers to FAPI, a high‑security profile built on OAuth 2.0 to strengthen financial‑grade APIs. It explains why FAPI was created, what security gaps it hardens, and the shift from bearer tokens to sender‑constrained tokens. It outlines the evolution from FAPI 1.0 to the simpler, more secure FAPI 2.0 and highlights key developer changes. The paper details FAPI’s dual‑layer security approach, covering token sender‑constraining, protecting issuance flows, and improving authorization through measures like pushed authorization requests, along with the resource server’s verification responsibilities.

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