[stormer78]

Defect

DTGCredential::verify_proof_with_public_key verified the Data Integrity proof under the key the caller passed, but never checked that the proof's verificationMethod belongs to the credential's issuer. A caller that resolves the method the proof names and then trusts issuer() accepted a credential naming any issuer, signed by any key. verify_grant_with_public_key already made this check; the credential-level entry point did not.

Fix

One private helper, check_proof_from_issuer, now runs after the signature in both public verification entry points:

Entry point	Before	After
DTGCredential::verify_proof_with_public_key	no binding	binding
verify_grant_with_public_key	binding (inline)	same binding, shared helper

authority::verify_chain and delegation::verify_chain check no signatures themselves (by design, documented); they rely on each link having gone through verify_proof_with_public_key, so they gain the binding through it. No other public function verifies a proof.

A method belongs to the issuer when:

• the DID before its # is exactly the issuer (did:x:a#key-1), or
• it is the issuer itself, with no fragment, or
• it is a bare #fragment, read against the issuer (previously refused by the grant path).

Comparison is verbatim (a DID URL with a query or path before the fragment is not the issuer); an empty issuer matches nothing. On the grant path the issuer may be a string or an object with an id.

Compatibility

• Not API-breaking. DTGCredentialError::ProofNotFromIssuer already existed and the enum is #[non_exhaustive]. No version bump here; CHANGELOG entry under [Unreleased].
• Behaviour change: a credential signed with a key whose id is not a method of the issuer no longer verifies. Two unit tests signed with randomly-named keys and were given issuer-bound key ids.

Tests

tests/issuer_binding.rs, each case against both entry points: another DID refused; a DID that merely extends the issuer's refused; a DID URL with a query refused; a method of the issuer accepted; the issuer itself as the method accepted; a relative #fragment accepted; object-form issuer bound by its id (accept and refuse).

Locally: cargo fmt --check, cargo clippy --all-targets --all-features -D warnings, cargo test --all-features, cargo test --no-default-features, cargo check on 1.95.0, cargo package, and both examples run.