Lesson 8 of 12 · 16 min read

Sender-Constrained Tokens: DPoP, mTLS and Token Exchange

A bearer token is honoured for whoever presents it, so a leaked token is a working credential. Sender-constrained tokens carry a confirmation claim naming a key, and the resource server checks that the caller proves possession: DPoP with a signed proof per request, mTLS with the client certificate on the connection. Binding stops replay of an exfiltrated token; it does not stop code that runs where the key is, or a forged token. Token exchange (RFC 8693) issues each hop a new, narrower, audience-bound token instead of passing one along.