feat: add wallet attestation-based client authentication

[leifj]

Summary

Enable wallets to authenticate without pre-registration in the static client map, by presenting a wallet-provider-signed attestation JWT (WIA) plus a proof-of-possession JWT, validated via delegation to the go-trust PDP.

Changes

• pkg/trust.WalletAttestationEvaluator: parses the attestation JWT, extracts wallet identity (from the x5c certificate chain when present, otherwise from iss per the IETF draft format), validates the PoP JWT against cnf.jwk, and delegates the trust decision to the PDP (role=wallet-provider)
• config.OAuthServer.AcceptWalletAttestation (accept_wallet_attestation): enables the feature; requires trust.pdp_url
• config.WalletAttestationPolicy (wallet_attestation_policy): optional SPOCP rules gating which attestation tiers (attestation_source) may request which scopes
• PAR and token endpoints fall back to wallet attestation when client_id is not found in the static clients map
• Standards-compliant transport: OAuth-Client-Attestation + OAuth-Client-Attestation-PoP HTTP headers per draft-ietf-oauth-attestation-based-client-auth-04 §3.1; legacy form-body client_assertion (no PoP) still accepted for backward compatibility

Verification Flow

1. Wallet sends the WIA + PoP as HTTP headers (or WIA via form-body client_assertion in legacy mode)
2. APIGW looks up client_id in the static client map → not found
3. APIGW validates the PoP JWT signature against the WIA's cnf.jwk and checks aud/exp
4. Wallet identity is derived from the WIA's x5c certificate chain when present (identity comes from the signature, not a self-asserted claim); iss, when present, is only used for routing and SPOCP authorization, and is cross-checked against the cert identity rather than trusted on its own
5. APIGW sends the WIA to the go-trust PDP with role=wallet-provider; PDP validates the wallet provider against trust lists/federation
6. If trusted (and, when configured, SPOCP authorizes the tier for the requested scope): wallet accepted as a public client (PKCE mandatory)

Configuration Example

apigw:
  trust:
    pdp_url: "https://trust.siros.se/pdp"   # Required
  delivery:
    openid4vci:
      accept_wallet_attestation: true        # Enable attestation
      wallet_attestation_policy:              # Optional SPOCP tier gating
        rules:
          - "(wallet (attestation_source ios_app_attest)(scope pid)(issuer *))"
      clients:                               # Static map still works as fallback
        legacy-wallet:
          redirect_uri: "..."
          scopes: [openid, pid]

The static clients map remains as a backward-compatible fallback. Existing pre-registered clients work unchanged.

Open question

There's an unresolved review thread on docs/TRUST_AND_IDENTITY.md about whether the "Requirements" section correctly reflects TS03 (identity from signature/cert only, iss used for routing/authz only) — flagging for @leifj to confirm before that doc section is finalized.

Context

Phase 3c of the client-id-strategy plan — eliminates the need for static client registration when wallet providers issue attestations.

[Copilot]

Pull request overview

This PR introduces wallet attestation–based client authentication so wallets can authenticate without pre-registration in the static OAuth client map, by verifying a wallet-provider-signed attestation JWT against trusted provider JWKS.

Changes:

• Adds a WalletAttestationVerifier and WalletProviderConfig to verify wallet-provider attestations via JWKS.
• Extends OAuth PAR handling to fall back to attestation when client_id is not in the static client map.
• Extends configuration (wallet_provider_trust, require_wallet_attestation) and request models to carry assertion parameters.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
pkg/openid4vci/authoriziation.go	Adds PAR request fields for carrying client assertion / attestation parameters.
pkg/oauth2/wallet_attestation_verifier.go	New verifier implementation for wallet-provider attestation JWTs using provider JWKS.
pkg/oauth2/wallet_attestation_verifier_test.go	Unit tests for the new wallet attestation verifier.
pkg/model/config.go	Adds config fields for trusted wallet providers and an enforcement flag.
internal/apigw/apiv1/handlers_oauth.go	Adds attestation fallback logic to PAR and token endpoints when client lookup fails.

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 11 comments.

[leifj]

This doesn't match with the TS03 specification iiuc - identity is derived from the signature only. Iss is only checked and used for routing and authz using spocp if present.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Comments suppressed due to low confidence (1)

docs/TRUST_AND_IDENTITY.md:85

• Implementation validates OAuth-Client-Attestation/...-PoP on both PAR and token endpoints (token falls back to attestation when client_id isn’t in the static map). The doc currently states the headers are sent only in the PAR request, which may mislead integrators who then omit them on the token request and get invalid_client.

1. Wallet sends `OAuth-Client-Attestation` (WIA JWT) and `OAuth-Client-Attestation-PoP` (PoP JWT) as HTTP headers in the PAR request per [draft-ietf-oauth-attestation-based-client-auth-04 §3.1](https://www.ietf.org/archive/id/draft-ietf-oauth-attestation-based-client-auth-04.html#section-3.1)

[leifj]

Addressed the remaining open review threads (commit 04a7a31):

• Require exp on the PoP JWT (jwt.WithExpirationRequired) — it was previously optional despite the function's own doc comment.
• Token endpoint: wallet-attestation policy authorization now checks the scope actually bound to the code (peeked non-destructively from AuthContext) instead of an empty/wildcard scope. The old Authorize(..., "", ...) effectively disabled scope-tier gating at the token endpoint, and — more importantly — pre-authorized_code requests never go through PAR, so the "scope was validated at PAR time" assumption didn't hold for that flow.
• Fixed a test helper silently ignoring the error from ecdsa.PublicKey.ECDH().
• Replaced the placeholder-string iat in the test WIA with a real numeric timestamp.
• Verified the several other open threads (PAR/Token PoP requirement, x5c fail-closed, issuerFromX5CLeaf docstring, require.NoError in tests, docs "How It Works" section) were already fixed by the earlier b307e817 commit and resolved those.
• Rewrote the PR description — it was describing an earlier design (WalletProviderTrust, RequireWalletAttestation, wallet_provider_trust) that doesn't match what actually shipped (accept_wallet_attestation, wallet_attestation_policy, PDP delegation).

Left open, needs @leifj's call: the thread on docs/TRUST_AND_IDENTITY.md (Requirements section) about whether identity should be described as coming from the signature/certificate only, with iss used solely for routing/authz via SPOCP per TS03 — vs. the doc's current wording that implies iss is required. The code already treats iss as optional when x5c is present (see the "may be absent in TS03 format" comment in wallet_attestation.go), so this looks like a doc-only fix, but I didn't want to rewrite the spec-compliance framing without confirmation.

All builds/tests green (go build ./..., go test ./...), gofmt clean on touched files.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (7)

internal/apigw/httpserver/endpoints_oauth.go:135

• OAuth-Client-Attestation and OAuth-Client-Attestation-PoP are set after Binding.Request, so they bypass any struct-tag validation. Adding a simple max-size check here (consistent with client_assertion's max=8192) would reduce the risk of oversized header inputs causing unnecessary work or memory pressure.

	// Extract OAuth-Client-Attestation headers (draft-ietf-oauth-attestation-based-client-auth-04 §3.1)
	request.ClientAttestation = c.GetHeader("OAuth-Client-Attestation")
	request.ClientAttestationPoP = c.GetHeader("OAuth-Client-Attestation-PoP")

pkg/trust/wallet_attestation.go:185

• PoP validation only checks that exp is not in the past and that iat is present. Without any freshness/max-lifetime constraint, a long-lived PoP can be replayed as a bearer credential for its full exp window, weakening proof-of-possession semantics. Consider enforcing a maximum validity window (e.g., exp-iat <= 5m) and rejecting iat values that are far in the past/future (beyond the existing leeway).

	// exp is required (jwt.WithExpirationRequired) and already validated by jwt.Parse (with leeway)
	// iat presence check
	if claims.IssuedAt == nil {
		return errors.New("PoP missing iat claim")
	}

docs/TRUST_AND_IDENTITY.md:105

• The Requirements section currently states that the attestation JWT must contain iss, but the implementation supports TS03-style attestations where iss may be absent and provider identity is derived from the x5c certificate chain. The doc should reflect that sub is required, and that provider identity comes from either iss (draft format) or x5c (TS03), with consistency checks when both are present.

- `trust.pdp_url` must be configured (PDP performs the trust decision)
- Wallet provider must be discoverable by the PDP (via OIDF, trust lists, or JWKS registry)
- Attestation JWT must contain `iss` (provider) and `sub` (wallet instance = `client_id`)

docs/TRUST_AND_IDENTITY.md:90

• The documented sequence says the APIGW validates the PoP JWT before sending the WIA to the PDP, but the implementation calls Evaluate (PDP trust decision) before validateAttestationPoP. Please update the step order (or wording) so the doc matches the actual flow.

1. Wallet sends `OAuth-Client-Attestation` (WIA JWT) and `OAuth-Client-Attestation-PoP` (PoP JWT) as HTTP headers in the PAR request per [draft-ietf-oauth-attestation-based-client-auth-04 §3.1](https://www.ietf.org/archive/id/draft-ietf-oauth-attestation-based-client-auth-04.html#section-3.1)
2. APIGW looks up `client_id` in static client map → not found
3. APIGW validates the PoP JWT signature against the WIA's `cnf.jwk` and checks `aud` matches this AS
4. APIGW sends the WIA to go-trust PDP with `role=wallet-provider`
5. PDP validates wallet provider's signature against trust lists/federation

pkg/trust/wallet_attestation.go:283

• parseAttestationIdentity introduces several security-relevant branches (x5c vs iss selection, fail-closed behavior when x5c is malformed, and iss↔cert consistency checks), but the accompanying tests only cover cnf.jwk extraction and PoP validation. Adding unit tests for the identity parsing paths (e.g., x5c-only TS03, iss-only draft, and mismatched iss vs x5c identity) would help prevent regressions.

// parseAttestationIdentity extracts identity from a WIA JWT.
// Handles two formats:
//   - If `iss` claim present: use as issuer (IETF draft format)
//   - If x5c header present and no iss: derive issuer from leaf cert (TS03 format)
func parseAttestationIdentity(attestation string) (*attestationIdentity, error) {

internal/apigw/apiv1/client.go:158

• When accept_wallet_attestation is set but apigw.trust.pdp_url is empty, wallet attestation is silently disabled (the if ... && pdpURL != "" guard just skips initialization). Given the config comment and PR description say pdp_url is required for this feature, this should fail fast (or at least log an explicit warning) to avoid operators believing attestation is enabled when it isn't.

	// Wallet attestation: enabled when accept_wallet_attestation + pdp_url are set
	if cfg.APIGW.Delivery.OpenID4VCI.AcceptWalletAttestation && pdpURL != "" {
		c.walletAttestationEvaluator = trust.NewWalletAttestationEvaluator(trustEvaluator)

internal/apigw/httpserver/endpoints_oauth.go:34

• OAuth-Client-Attestation and OAuth-Client-Attestation-PoP are populated after Binding.Request, so they bypass the usual request validation (size limits / printability). It would be easy to trigger extra parsing work or memory pressure with oversized header values. Consider enforcing the same max length you use for client_assertion (8192) before assigning these headers onto the request.

This issue also appears on line 132 of the same file.

	// Extract OAuth-Client-Attestation headers (draft-ietf-oauth-attestation-based-client-auth-04 §3.1)
	request.ClientAttestation = c.GetHeader("OAuth-Client-Attestation")
	request.ClientAttestationPoP = c.GetHeader("OAuth-Client-Attestation-PoP")

[leifj]

Done (commit e02e3a8) — moved accept_wallet_attestation/wallet_attestation_policy from delivery.openid4vci into a new trust.wallet_attestation block (enabled/policy), alongside pdp_url:

apigw:
  trust:
    pdp_url: "https://trust.siros.se/pdp"
    wallet_attestation:
      enabled: true
      policy:
        rules:
          - "(wallet (attestation_source ios_app_attest)(scope pid)(issuer *))"

This config hasn't shipped anywhere yet, so the move was free. Updated the one call site, the TRUST_AND_IDENTITY.md example, and regenerated CONFIGURATION.md. go build ./... and go test ./... pass.

[sonarqubecloud]

Quality Gate passed

Issues
6 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud