RFC 9449 Quiz

**Explanation:** A: The resource server still receives the access token. B: A copied token alone is insufficient when the presenter lacks the private key. C: DPoP constrains presentation and does not expand authorization scope.

**Explanation:** A: The embedded public key is not automatically bound to a registered client identity. B: Token-endpoint DPoP proofs can exist without an access token and proof validity still is not client authentication. C: Additional OAuth and application checks establish client identity and permitted action.

**Explanation:** A: The alg must be asymmetric, supported, registered, and acceptable to policy. B: The none algorithm is explicitly disallowed. C: DPoP requires asymmetric signatures and the jwk must not include a private key.

**Explanation:** A: Base DPoP does not provide whole-message integrity. B: The htm and htu claims bind the proof to method and URI while other claims provide time and uniqueness. C: The ath claim binds a token when present but method and URI are also covered.

**Explanation:** A: ath is a hash binding inside the signed proof and is not token encryption. B: TLS server identity selection is outside the ath claim. C: The token hash prevents substituting another token under a captured proof.

**Explanation:** A: RFC 9449 Section 4.3 requires the resource server to match `htm` and `htu`, validate `ath` against the presented access token, and verify that the proof key matches the token's confirmation binding. The stem states that the other Section 4.3 checks already passed. B: `jti` alone does not bind the method, URI, access-token value, or confirmation key. C: A valid signature is necessary but does not replace validation of the signed claims.

**Explanation:** A: kid is a key identifier and not the nonce claim. B: When the server provides a nonce, the proof must echo it in the signed payload. C: A new server nonce prevents reuse of a proof that lacks the current value.

**Explanation:** A: The token itself is still transmitted and ath does not provide channel confidentiality. B: A non-extractable key does not authenticate the server or encrypt the HTTP exchange. C: RFC 9449 explicitly treats DPoP as an additional control and not a transport substitute.

**Explanation:** A: A server supporting DPoP must not bypass the key proof by accepting the bound token as Bearer. B: Lifetime validity does not satisfy the token's sender constraint. C: The resource server cannot rewrite the authorization server's token binding.

**Explanation:** A: Preventing token-only use is the principal benefit of sender constraining. B: RFC 9449 Section 11.4 explains that a non-extractable key may resist export but not malicious use by code executing in the client. C: DPoP does not disable TLS server authentication.