Internal Service Authentication

Fission signs internal control-plane RPCs with application-layer HMAC authentication, enabled by default since v1.23.0. This is distinct from the end-user function-invocation authentication (JWT, opt-in), which protects function invocations rather than in-cluster RPCs.

What it protects

Five internal channels now require signed requests when internalAuth.enabled=true:

Each pair derives a per-service key via HKDF from a single chart-managed master secret, so one toggle gates all five channels atomically.

Key behavioral change in v1.23.0

The router now binds two listeners:

• Public listener (port 8888) — serves user HTTPTrigger paths, /router-healthz, /_version, and (when enabled) the JWT-based function-invocation auth.
• Internal listener (port 8889) — serves /fission-function/<ns>/<name> only, gated by NetworkPolicy plus HMAC verification.

/fission-function/<ns>/<name> no longer exists on the public listener. This closes GHSA-3g33-6vg6-27m8 — previously anyone reachable to the public router URL (e.g. via Ingress) could invoke any function by guessing its name, bypassing all HTTPTrigger host/path/method gates.

Any external tooling that today curls /fission-function/... against the public router URL will receive 404 after upgrading. The public listener is unchanged for user HTTPTrigger traffic.

Default install

internalAuth.enabled defaults to true from v1.23.0 onwards:

helm install fission fission-charts/fission-all -n fission --create-namespace

The chart materialises a Secret/fission-internal-auth with an auto-generated 32-byte master key. The same value is preserved across helm upgrade runs. Every Fission control-plane component (storagesvc, executor, router, buildermgr, and the rest) and every dynamically-created builder/function pod mounts the master via environment variable; each signer/verifier pair derives its own per-service key.

Bring your own master secret

Pass an explicit master secret at install time to skip the auto-generated key:

helm install fission fission-charts/fission-all -n fission \
  --set internalAuth.secret="$(openssl rand -base64 32)"

If internalAuth.secret is set, the chart honours it instead of auto-generating one.

Disable everywhere

Turn off signing across all five channels at install time:

helm install fission fission-charts/fission-all -n fission \
  --set internalAuth.enabled=false

With enabled=false the chart skips the Secret and the env mounts. Every signer/verifier short-circuits to pass-through — no signing, no verification — so the cluster falls back to NetworkPolicy + namespace isolation alone for in-cluster trust.

This is the recommended setting if you rely on stock upstream KEDA connector images (ghcr.io/fission/keda-kafka-http-connector and the other keda-*-http-connector images) — see Caveats below.

The router’s two-listener split is independent of this toggle: /fission-function/<ns>/<name> remains on the internal listener regardless. With internalAuth.enabled=false the internal listener still accepts unsigned requests; with internalAuth.enabled=true it requires signatures.

Master-secret rotation

The master secret can be rotated without downtime using the oldSecret overlap field:

# Step 1 — pin the live secret as `oldSecret` so verifiers accept both.
LIVE=$(kubectl -n fission get secret fission-internal-auth -o jsonpath='{.data.secret}' | base64 -d)
helm upgrade fission fission-charts/fission-all -n fission \
  --set internalAuth.oldSecret="$LIVE"

# Step 2 — roll in the new master.
helm upgrade fission fission-charts/fission-all -n fission \
  --set internalAuth.secret="$(openssl rand -base64 32)"

# Step 3 — wait for every Fission deployment to finish rolling.

# Step 4 — drop the old secret.
helm upgrade fission fission-charts/fission-all -n fission \
  --set internalAuth.oldSecret=""

Because every per-service key is derived from the master via HKDF, this single sequence rotates the key for all five channels atomically.

Toggle interaction matrix

The verifier (server) and signer (client) toggles are set independently per rollout, so mixed states are possible; this table shows the outcome of each combination:

The chart applies the toggle wholesale, so the “ON / OFF” failure mode only surfaces during hand-edited deployments, in-flight helm upgrade rollouts where some pods haven’t rolled yet, or external tooling that signed against an unconfigured CLI.

Caveats

KEDA connector signing gap

Upstream ghcr.io/fission/keda-kafka-http-connector (and the other keda-*-http-connector images) do not yet sign their /fission-function/... invocations. With internalAuth.enabled=true (the default), KEDA-driven message-queue triggers will receive 401 from the router internal listener.

Operators have two options until signing-aware KEDA images ship:

1. Build signing-aware connector images (recommended long-term). The signer primitive lives in pkg/auth/hmac in the Fission repo.
2. Set internalAuth.enabled=false and rely on NetworkPolicy alone for the KEDA traffic. The internal listener still hosts /fission-function/<ns>/<name> but does not enforce signatures.

ROUTER_INTERNAL_URL

Services that publish to the router internal listener (kubewatcher, timer, mqt-fission-kafka, mqt-keda) now read ROUTER_INTERNAL_URL. The chart sets it to http://router-internal.<namespace>:<router.internalPort> (port 8889 by default) using the dedicated router-internal Service. If you customise the router Service name, namespace, or router.internalPort, set this env override accordingly.

Reference

• GHSA-3g33-6vg6-27m8 — router public-listener function-invocation exposure (fixed by the two-listener split)
• PR #3368 — initial HMAC wiring on storagesvc
• PR #3369 — extension to fetcher, builder, executor, router-internal