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Add client-certificate authorization mode for metrics endpoint - #3936
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Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 2 remain after this review. 📝 WalkthroughWalkthroughThe metrics and health server adds optional authorization by verified client certificate. The catalog and OLM commands expose settings for this mode and for allowed certificate common names. CA bundle loading now rejects bundles without parseable certificates and retains the current pool after an invalid reload. ChangesMetrics client-certificate authorization
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant HTTPClient
participant requireVerifiedClientCert
participant verifyPeerCertificate
participant MetricsHandler
HTTPClient->>requireVerifiedClientCert: Send metrics request
requireVerifiedClientCert->>verifyPeerCertificate: Verify certificate against current CA pool
verifyPeerCertificate-->>requireVerifiedClientCert: Return verification result
alt Certificate verified and common name allowed
requireVerifiedClientCert->>MetricsHandler: Forward request
MetricsHandler-->>HTTPClient: Return response
else Certificate missing or not verified
requireVerifiedClientCert-->>HTTPClient: Return HTTP 401
else Common name not allowed
requireVerifiedClientCert-->>HTTPClient: Return HTTP 403
end
Merge Risk: ⚪ Minimal · up to The previously identified CA-bundle and persistent-connection risks are addressed. No actionable merge-blocking issue remains after normal checks. Security Architecture ReviewSecurity architecture risk: 🟡 Moderate · up to The new mode has explicit TLS requirements and checks certificates on every metrics request. However, some CA-bundle changes are ignored, allowing previously trusted certificates to retain access after an intended rotation. Exposure is limited to metrics on operators where the new mode is enabled. Retained concerns
Security review detailsSecurity Blast Radius
Security Findings and Attack Paths
Trust Boundaries and Controls
Resilience and Maintainability Implications
Hardening Proposals
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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Inline comments:
Review comments at @pkg/lib/server/server.go:
- Around line 165-166: Update NewCertPoolStore and storeCABundle to reject CA
bundles when AppendCertsFromPEM reports no parseable certificates, returning an
error and preserving the existing usable pool on invalid updates.
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cmd/catalog/main.gocmd/catalog/start.gocmd/olm/main.gopkg/lib/server/server.gopkg/lib/server/server_clientca_test.go
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Inline comments:
Review comments at @pkg/lib/server/server.go:
- Line 308: Update the metrics handler’s check around r.TLS.VerifiedChains to
revalidate the peer certificate against the current client CA pool on every
request, or close existing connections when that pool changes; do not rely only
on a non-empty verified chain from the original handshake.
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cmd/catalog/main.gocmd/catalog/start.gocmd/olm/main.gopkg/lib/server/server.gopkg/lib/server/server_clientca_test.go
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Inline comments:
Review comments at @pkg/lib/server/server.go:
- Around line 369-373: Add read locking inside certPoolStore.GetCertPool so
reads of c.certpool are synchronized with the replacement write in
storeCABundle; keep the lock held until the pool pointer has been read.
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| // 1. client-certificate authorization (mutual TLS): scrapers are authorized | ||
| // by verifying their client certificate against the configured client CA | ||
| // bundle. Used when the scraper authenticates with a client certificate | ||
| // rather than a bearer token. | ||
| // 2. token-based authentication/authorization: scrapers are authenticated and | ||
| // authorized via TokenReview/SubjectAccessReview against the kubeConfig's | ||
| // API server. This is the default on standalone clusters. |
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In theory, these two options don't need to be mutually exclusive (whereas the 3rd option is). It's possible to request a certificate from the client, and rather than having the TLS stack reject the connection because the client does not provide a certificate, the server itself can ask the TLS stack what the certificate is, and determine if it's valid. That way, the token-based authentication could also happen. So the process would be:
TLS Handshake:
S>C: CertificateRequest
C>S: Certificate (0 or more certificates)
TLS stack configured to not require a certificate.
Server:
If certificate auth is configured, get the client certificate from the stack and validate it (the stack may already do this). If it's valid and passes the CN check, then authentication passes.
If token-based authentication is configured, check the token.
Otherwise, fail authentication.
But I think an either-or is fine for an initial fix.
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One thing we need to consider if we ever want a unified approach is the HCP case where you have two kube api servers. So, the question becomes which one do you use for the SAR.
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/approve While it would be great to be able to support cert and token-based authentication simultaneously, it it's necessary at this time. I would like to see the 401/403 returns reconciled, to avoid information leakage, but that's relatively minor. |
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: tmshort The full list of commands accepted by this bot can be found here. The pull request process is described here DetailsNeeds approval from an approver in each of these files:
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/hold as I'd like to address a couple of these comments |
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The olm and catalog operators serve metrics over a TLS endpoint secured with controller-runtime's WithAuthenticationAndAuthorization filter, which authenticates scrapers via a bearer token (TokenReview) and authorizes them via SubjectAccessReview against the operator's kubeConfig API server. A presented client certificate is only used at the transport layer (VerifyClientCertIfGiven) and is not treated as an authentication identity. This breaks metrics scraping in environments where the scraper authenticates with a client certificate rather than a bearer token, and where the operator's kubeConfig does not point at the same API server that can authenticate the scraper's identity - so TokenReview/SubjectAccessReview cannot authorize the scraper and every scrape is rejected with 401. Add an opt-in --client-ca-authorization flag (olm and catalog). When enabled, the /metrics endpoint is authorized by verifying the scraper's client certificate (mutual TLS) against the configured --client-ca bundle instead of using the token-based filter; requests without a client certificate receive 401. The certificate is re-verified against the current client CA bundle on every request (not only at TLS handshake), so that a rotation of the client CA bundle takes effect immediately even on a reused keep-alive connection. Certificate-less health probes on other endpoints are unaffected. Add an optional --client-ca-allowed-cn flag to further restrict authorization to certificates whose common name is in the given set. A certificate that verifies against the CA but whose common name is not in the set is rejected with the same 401 and message as a failed CA verification, so the rejection reason is not leaked to the client (the common name is recorded in the server log). When empty, any certificate that verifies against the client CA bundle is authorized - the CA bundle itself is the allowlist. Set a ReadHeaderTimeout and IdleTimeout on the metrics server to bound slow-header and idle keep-alive connections; read/write timeouts are left unset so long-running pprof profiles are not truncated. The feature is disabled by default, so existing deployments keep the existing token-based behavior. It requires TLS (--tls-cert/--tls-key) and a client CA bundle (--client-ca), and fails closed otherwise. Also harden the client CA loader: NewCertPoolStore and storeCABundle previously ignored the result of AppendCertsFromPEM, so a readable but empty or invalid CA bundle produced an empty cert pool. With client-certificate authorization enabled, an empty pool can verify no client certificate, so every scrape would be rejected while the operator reports healthy. Fail closed on startup when the bundle has no parseable certificates, and preserve the existing usable pool when a bundle update is invalid. Take the read lock in GetCertPool so per-request reads are synchronized with bundle-rotation writes. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Signed-off-by: Per G. da Silva <pegoncal@redhat.com>
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/unhold |
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My approval still stands after the most recent changes. Need someone else for the LGTM (but it looks LGTM to me). |
2 participants
Problem
The olm and catalog operators serve metrics over a TLS endpoint secured with controller-runtime's
filters.WithAuthenticationAndAuthorization(pkg/lib/server/server.go). That filter authenticates scrapers via a bearer token (TokenReview) and authorizes them via SubjectAccessReview against the operator's kubeConfig API server. A presented client certificate is only used at the transport layer (VerifyClientCertIfGiven) and is not treated as an authentication identity.This breaks metrics scraping in environments where:
In that case TokenReview/SubjectAccessReview cannot authorize the scraper, so every scrape is treated as anonymous and rejected with 401, and the targets report down indefinitely.
Change
Add an opt-in
--client-ca-authorizationflag (olm and catalog). When enabled, the/metricsendpoint is authorized by verifying the scraper's client certificate (mutual TLS) against the configured--client-cabundle, instead of the token-based filter. Requests without a client certificate receive 401.--client-cabundle takes effect immediately — even on a reused keep-alive connection whose handshake-timeVerifiedChainspredates the rotation. Certificate-less health probes on other endpoints are unaffected.--client-ca-allowed-cnfurther restricts authorization to certificates whose common name is in the given set. A certificate that verifies against the CA but has a disallowed common name is rejected with the same 401 and message as a failed CA verification, so the rejection reason is not leaked to the client (the common name is logged server-side). When empty, any certificate that verifies against the client CA bundle is authorized — the CA bundle itself is the allowlist.ReadHeaderTimeout/IdleTimeoutare set on the metrics server to bound slow-header and idle keep-alive connections (read/write timeouts left unset so long-running pprof profiles aren't truncated).--tls-cert/--tls-key) and--client-ca; fails closed otherwise.Also harden the client CA loader (
pkg/lib/filemonitor):NewCertPoolStoreandstoreCABundlepreviously ignored the result ofAppendCertsFromPEM, so a readable but empty/invalid CA bundle produced an empty pool. With client-certificate authorization enabled, an empty pool verifies no client certificate — every scrape would be rejected while the operator reports healthy. Now it fails closed on startup when the bundle has no parseable certificates, and preserves the existing usable pool when a bundle update is invalid.GetCertPooltakes the read lock so per-request reads are synchronized with bundle-rotation writes.Testing
pkg/lib/server/server_clientca_test.go: the middleware (no client cert → 401; cert verified against the current pool → pass; cert that no longer verifies against the current pool, simulating CA rotation → 401; CN allow/deny → 200/401), the configuration wiring (success with TLS+client-ca and no kubeConfig), and fail-closed on missing TLS / missing client-ca (asserting the specific errors).pkg/lib/filemonitor/cabundle_updater_test.go: valid bundle loads, a bundle with no parseable certificates is rejected, an invalid update preserves the prior pool, and concurrentGetCertPool/storeCABundleaccess is race-free undergo test -race.go build ./cmd/...,go vet,gofmt, andgo test -race ./pkg/lib/server/... ./pkg/lib/filemonitor/...all pass.Summary by CodeRabbit
New Features
Bug Fixes