Expiration date is ignored by verify method

[jceb]

I noticed that the expiration_date property in a Verifiable Credential is ignored by the verify method. Example:

didkit key generate ed25519 > key.jwk
DID=$(didkit key-to-did -k key.jwk)
cat <<EOF > expired-credential.json
{
  "@context": [
    "https://www.w3.org/2018/credentials/v1"
  ],
  "id": "uuid:49387f58-c0d9-4b14-a4f4-bc31a021d925",
  "type": ["VerifiableCredential"],
  "issuer": "$DID",
  "issuanceDate": "2021-12-31T00:00:00Z",
  "expirationDate": "2022-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "$DID"
  }
}
EOF
didkit vc-issue-credential -k key.jwk -p assertionMethod  < expired-credential.json > expired-credential-signed.json
didkit vc-verify-credential < expired-credential-signed.json
{"checks":["proof"],"warnings":[],"errors":[]}

This behavior makes sense to me as it seems like the verify method seems to be operating only on the proof and I might want to have additional business logic that deals with expired credentials differently than with credentials that have invalid proofs. However, I'd find it helpful if this behavior is highlighted in the documentation. In addition, it would be great to have an additional method that validates/verifies expiration and not before dates.