feat(signing): L1 signing — RFC 9421, KMS providers, JWKS, webhook verification by MichielDean · Pull Request #32 · adcontextprotocol/adcp-sdk-java

MichielDean · 2026-06-17T20:44:42Z

Summary

Track 4 (L1 Signing) — complete RFC 9421 message signing and verification for the AdCP Java SDK.

Core SPI (`adcp` module)

SigningProvider / VerificationKeyResolver — SPI interfaces via META-INF/services/
SigningContext — tenant-aware key selection (D22): AdcpUse use(), @Nullable TenantId tenant(), @Nullable PrincipalRef principal()
AdcpUse enum — REQUEST_SIGNING, WEBHOOK_SIGNING with wire name mapping
VerificationKeyLookup — sealed interface: Found(key, tenant, principal) / Missing(kid)
VerificationResult — sealed interface: Valid / Invalid(errorCode, reason, failedStep)
VerificationException — typed errors matching webhook_signature_* taxonomy

RFC 9421 Canonicalizer (`adcp-server` module)

Hand-rolled implementation per RFC 9421 §2.5 (no org.tomitribe:http-signatures dependency)
93 conformance tests against AdCP test vectors (webhook signing positive/negative, request signing, URL canonicalization)
Rfc9421Signer — produces Signature-Input, Signature, Content-Digest headers
Rfc9421Verifier — full 13-step verification checklist
AdcpSignatureProfile — required components, algorithms, tags, replay window enforcement
HeaderNormalizer — RFC 9421 header name/value normalization
ContentDigest — RFC 9530 SHA-256/512 content digest
IDNA/UTS#46 hostname canonicalization

Signing Providers

InProcessSigningProvider — JCA Ed25519, ES256, ES384 (no Bouncy Castle in core)
InProcessKeyGenerator — Ed25519/ES256/ES384 keypair generation
AwsKmsSigningProvider — AWS KMS with lazy-init, tripwire verification, ECDSA DER-to-raw conversion
GcpKmsSigningProvider — GCP KMS with lazy-init, tripwire, service account credentials
BouncyCastleSigningProvider — stub (FIPS environments only, UnsupportedOperationException)

Verification & Key Resolution

JwksVerificationKeyResolver — SPI entry point
StaticJwksResolver — in-memory from pre-loaded JWKS
CachingJwksResolver — HTTP-fetching with 30s cooldown, single-flight dedup
BrandJsonJwksResolver — 3-hop resolution (brand.json → agent → jwks_uri)
SsrfJwksUriValidator — HTTPS enforcement, private IP rejection, DNS rebinding defense
JwkParser — Ed25519, EC (P-256/P-384), RSA JWK parsing with adcp_use and key_ops validation

Webhook Signing

WebhookSigner seam interface for Track 6 (async-l3)
DefaultWebhookSigner — implementation using Rfc9421Signer
LegacyHmacWebhookVerifier — deprecated HMAC-SHA256 (removed in AdCP 4.0), timing-safe comparison, rotation support
StandardWebhooksVerifier — Svix/Resend v1 interop
WebhookChallenge + WebhookChallengeVerifier — endpoint proof-of-control

Key Management

InMemoryReplayStore — nonce dedup with 300s TTL eviction
InMemoryRevocationStore — revoked kid tracking with staleness detection
CachingRevocationChecker — JWS-verified revocation list fetcher with grace window
SigningKeyGenerator — Ed25519/ES256/ES384 keypair generation with JWK output
KeyOriginConsistencyCheck — ADCP #3690 eTLD+1 key origin verification
ETldPlusOne — public suffix extraction utility

JWS Verification

JwsVerifier — compact and JSON general JWS verification
JwsDocument — parsed JWS record

CLI

signing-probe subcommand — pre-deploy KMS connectivity and key usability check

Modules

adcp — core SPI interfaces
adcp-server — canonicalizer, providers, verification, webhook
adcp-signing-aws-kms — AWS KMS provider (real implementation)
adcp-signing-gcp-kms — GCP KMS provider (real implementation)
adcp-signing-bouncycastle — BC FIPS provider (stub)
adcp-cli — signing-probe command

Tests

226+ tests across all signing modules, including full conformance coverage against AdCP webhook signing and request signing test vectors.

Design Decisions

Hand-rolled canonicalizer (not org.tomitribe:http-signatures) — Cavage draft ≠ RFC 9421
No Bouncy Castle in core — JDK 21 has Ed25519 natively; BC only in optional FIPS module
Lazy-init for KMS — no gRPC retries on boot; pre-deploy probe is a separate CLI
Tripwire verification — committed SPKI fingerprint compared against KMS-returned key at first sign
ECDSA DER-to-raw — AWS/GCP KMS return DER-encoded signatures; RFC 9421 requires raw (r||s) format
SigningContext-based API (D22) — no single-arg forUse(); tenant and principal nullable until v0.3

Known Limitations

AccountStore → SigningContext tenant resolution wiring deferred to Track 5 (v0.3)
Postgres-backed ReplayStore deferred to Track 6 (async-l3)
adcp-keygen CLI wrapper not yet added (trivial, can land anytime)

…ntext, VerificationKeyResolver)

…ormance tests

…verification round-trip tests Track 4 (L1 Signing) implementation: - InProcessSigningProvider: JCA Ed25519/ES256/ES384 signing via SigningProvider SPI, delegates to Rfc9421Canonicalizer for signature base construction - InProcessKeyGenerator: test keypair generation utility (Ed25519, ES256, ES384) for development/testing - InProcessVerificationProvider: verification path using Rfc9421Verifier with AdCP profile validation - WebhookSigner/DefaultWebhookSigner: seam interface for Track 6 (async-l3) webhook signing, applies AdCP webhook-signing profile - WebhookSigningResult: record for signed webhook headers - Tests: signing/verification round-trip for Ed25519 and ES256, key generation, webhook signer seam

…wire, and ECDSA DER conversion

…lidation, and brand.json walk - JwkParser: parse Ed25519, EC (P-256/P-384), and RSA JWKs into VerificationKey - StaticJwksResolver: in-memory kid lookup from pre-loaded JWKS - CachingJwksResolver: HTTP-fetching with 30s cooldown, single-flight dedup - BrandJsonJwksResolver: 3-hop resolution (brand.json → agent → jwks_uri) - SsrfJwksUriValidator: HTTPS enforcement, private IP rejection, redirect:manual - JwksDocument: parsed JWKS with per-kid index and lastFetched timestamp - JwksResolutionException: unchecked exception for JWKS fetch failures - SsrfBlockedException: made constructor public for JWKS validator tests

…r nonce dedup and key revocation

…r generation

…izer

gitguardian · 2026-06-17T20:45:21Z

⚠️ GitGuardian has uncovered 3 secrets following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secrets in your pull request

GitGuardian id	GitGuardian status	Secret	Commit	Filename
34069021	Triggered	Generic High Entropy Secret	`f3d9c7b`	adcp-server/src/test/java/org/adcontextprotocol/adcp/server/signing/webhook/StandardWebhooksVerifierTest.java	View secret
34069022	Triggered	Generic High Entropy Secret	`f3d9c7b`	adcp-server/src/test/java/org/adcontextprotocol/adcp/server/signing/webhook/StandardWebhooksVerifierTest.java	View secret
34069023	Triggered	Generic High Entropy Secret	`f3d9c7b`	adcp-server/src/test/java/org/adcontextprotocol/adcp/server/signing/webhook/StandardWebhooksVerifierTest.java	View secret

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aao-ipr-bot · 2026-06-17T20:45:23Z

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aao-ipr-bot · 2026-06-17T21:28:48Z

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The compliance test vectors in adcp-server/src/test/resources/compliance/ contain intentionally public test keys with _private_d_for_test_only fields. These are for signer/verifier round-trip conformance testing and MUST NOT be used in production. The keys.json files carry explicit warnings in their _WARNING and fields.

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…h presence) The .gitguardian file only takes effect when present on the default branch. For now, the test key findings will be marked as false positives via the GitGuardian dashboard. The keys.json files contain intentionally public test keys from the AdCP compliance suite with explicit warnings.

aao-ipr-bot · 2026-06-17T21:32:35Z

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bokelley

Thanks for the large signing implementation. I reviewed the verifier, signing providers, JWKS/brand.json resolution, revocation handling, and webhook helpers. I think this needs another pass before merge; the targeted tests pass locally, but there are several correctness/security issues that the current coverage does not catch.

Findings:

[P1] Malformed signature inputs can throw instead of returning VerificationResult.Invalid.
adcp-server/src/main/java/org/adcontextprotocol/adcp/server/signing/Rfc9421Verifier.java:100 parses created/expires with Long.parseLong outside a catch, and extractSignatureBytes can throw from Base64.getUrlDecoder().decode(...) at line 364. A bad remote header can therefore become a verifier exception/500 instead of a signature rejection. Please keep all wire-format failures on the VerificationResult.Invalid path.
[P1] Empty webhook bodies cannot be signed correctly.
Webhook signing requires content-digest, but DefaultWebhookSigner.java:44 and InProcessSigningProvider.java:77 only add it when body.length > 0. For WEBHOOK_SIGNING, the covered component list still includes content-digest, so empty-payload webhooks either fail canonicalization or skip digest validation. The digest of an empty byte array is still a valid required Content-Digest value.
[P1] brand.json JWKS URI rotation is broken.
In BrandJsonJwksResolver.java, selectedJwksUri = jwksUri is assigned at line 214 before comparing at line 218, so the resolver replacement condition never detects a changed URI once innerResolver exists. If brand.json rotates to a new jwks_uri, the process can keep using the stale resolver until restart. Capture the previous selected URI before assignment, or compare against the existing resolver state.
[P2] Standard Webhooks secret padding is incorrect.
StandardWebhooksVerifier.java:65 uses "=".repeat((-payload.length()) % 4). Java preserves the negative remainder, so lengths where padding is needed can throw IllegalArgumentException: count is negative. Use (4 - payload.length() % 4) % 4 instead, and add an unpadded secret test for non-multiple-of-4 lengths.
[P2] Revocation stale handling does not match the result API.
CachingRevocationChecker.check returns RevocationResult, and the class docs say stale lists return RevocationResult.Stale, but ensureFresh() throws RevocationListStaleException from line 132. Callers using the sealed result API will not see the advertised Stale result. Please either return RevocationResult.Stale from check or change the API/docs/tests to make stale an exception path consistently.

Local verification run:

./gradlew :adcp-server:test :adcp-signing-aws-kms:test :adcp-signing-gcp-kms:test
BUILD SUCCESSFUL in 2m 57s

Lobsterdog Contributors added 18 commits June 16, 2026 22:28

feat(signing): add core L1 signing SPI interfaces (AdcpUse, SigningCo…

ab1e729

…ntext, VerificationKeyResolver)

feat(signing): add RFC 9421 canonicalizer, signer, verifier, and conf…

3b3ad10

…ormance tests

feat(signing): add KMS provider module skeletons and BouncyCastle stub

8bfda3b

docs(signing): add RFC 9421 canonicalizer design spec

19ed167

feat(signing): implement AWS KMS SigningProvider with lazy-init, trip…

28697e5

…wire, and ECDSA DER conversion

feat(signing): implement GCP KMS SigningProvider with lazy-init, trip…

3578adf

…wire, and ECDSA DER conversion

feat(signing): add InMemoryReplayStore and InMemoryRevocationStore fo…

689d122

…r nonce dedup and key revocation

feat(signing): add pre-deploy KMS probe CLI command

82802fa

feat(signing): add SigningKeyGenerator for Ed25519/ES256/ES384 keypai…

3ce0955

…r generation

feat(signing): add IDNA hostname canonicalization to Rfc9421Canonical…

d98cf3e

…izer

feat(signing): add key origin consistency check and eTLD+1 utility

15ebe32

feat(signing): add JWS verification for revocation lists

7147c61

feat(signing): add CachingRevocationChecker with JWS verification

fada93f

feat(signing): add legacy HMAC-SHA256 webhook verification (deprecated)

9d4f17d

feat(signing): add Standard Webhooks v1 interop verifier

f3d9c7b

feat(signing): add webhook challenge proof-of-control

5ee26c1

MichielDean requested a review from bokelley as a code owner June 17, 2026 20:44

chore: add gitguardian config to ignore test key fixtures

7165a40

bokelley requested changes Jun 17, 2026

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feat(signing): L1 signing — RFC 9421, KMS providers, JWKS, webhook verification#32

feat(signing): L1 signing — RFC 9421, KMS providers, JWKS, webhook verification#32
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feat/l1-signing-track4

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MichielDean commented Jun 17, 2026

Summary

Core SPI (adcp module)

RFC 9421 Canonicalizer (adcp-server module)

Signing Providers

Verification & Key Resolution

Webhook Signing

Key Management

JWS Verification

CLI

Modules

Tests

Design Decisions

Known Limitations

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Core SPI (`adcp` module)

RFC 9421 Canonicalizer (`adcp-server` module)

gitguardian Bot commented Jun 17, 2026 •

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