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92. OpenAI WIF credential delivery — runner-side exchange, run-scoped provider ​

Date: 2026-08-27

Status ​

Accepted

Context ​

The pi runtime (#6464) serves Claude, Grok and Gemini on Vertex, but no OpenAI model (#6532). OpenAI now offers Workload Identity Federation: a GitHub Actions job exchanges its OIDC JWT at POST https://auth.openai.com/oauth/token for an opaque Bearer access token that lives at most one hour — and no longer than the GitHub assertion it was exchanged from, which is minutes.

The token is a plain header credential, which means fullsend can run GPT models with no OpenAI credential inside the sandbox at all — ADR 0025 credential-delivery tier 2, one tier above today's Vertex path (which puts a real GitHub OIDC token and an external_account file on the sandbox filesystem).

Alternatives considered ​

  1. inference.local — at OpenShell 0.0.115 (the pinned version) this is a cluster-global route: one provider and one model per gateway, applied to every sandbox. fullsend runs on shared gateways (the GitLab runner VM's persistent gateway, local dev, parallel eval cases), so concurrent runs with different models or service accounts would race. Rejected.

  2. Dynamic token_grant — the supervisor mints a SPIFFE JWT-SVID as an RFC 7523 client assertion; OpenAI's exchange needs a GitHub-issued JWT plus identity_provider_id/service_account_id in a JSON body. Rejected.

  3. In-sandbox exchange — ACTIONS_ID_TOKEN_REQUEST_URL/_TOKEN are runner-only by design (oidcDenyKeys, internal/cli/run.go, #5832 / ADR 0073), and pi's built-in openai provider has no WIF concept. Rejected.

Decision ​

Runner-side exchange with a run-scoped OpenShell provider:

  1. The runner exchanges the GitHub OIDC JWT for an OpenAI access token before sandbox creation (internal/inference/openaiwif/).
  2. A run-scoped provider (openai-<suffix>) carries the token as a bare-key credential, never expanded through os.ExpandEnv (the opaque token may contain $). The provider has --credential-expires-at set (the token's own expiry, or a bounded lifetime for a static OPENAI_API_KEY from the runner environment) and is deleted in deferred cleanup regardless of --keep-sandbox; a provider whose expiry cannot be set is deleted immediately.
  3. The fullsend-openai OpenShell profile scopes egress to POST /v1/responses on api.openai.com for **/node binaries.
  4. The pi runtime gate writes the placeholder the sandbox environment carries for OPENAI_API_KEY into pi's auth.json (an openaiapi_key entry) before the agent-writable .env is sourced, and pi is started without --api-key. pi's AuthStorage re-reads that file whenever its revision changes and resolves the key per request (packages/coding-agent/src/core/auth-storage.ts, model-registry.ts at 0.84.3), so after each refresh the runner re-runs the same seed through sandbox exec — an exec'd shell's environment holds the new placeholder, the runner never learns the opaque revision — and the running iteration's next request carries the new credential. This is the only hand-off that works on OpenShell 0.0.115, where a revision-scoped placeholder stays pinned to the value of the generation it was issued for and the unrevisioned alias is refused for an endpoint-bound credential (see Consequences). A config-dir integrity guard (exit 98 when models.json exists, or auth.json is anything but pi's own {} or exactly the seeded placeholder entry) closes the redirect vector even with hooks disabled; it runs before .env is sourced and again after it behind unset -f test command grep tr, with the runner-owned config paths re-exported in between, so neither a sourced shell function nor a rewritten PI_CODING_AGENT_DIR can defeat it.
  5. Before the agent starts, the run reads the sandbox's effective policy and refuses to continue when any rule admits api.openai.com:443 without L7 inspection (no protocol, or tls: skip): since OpenShell 0.0.110 the proxy will not inject a provider credential over such a route, and the base sandbox image's default policy ships exactly that shape in its codex rule. The fleet's harnesses carry policy: policies/base.yaml, which has no network rules of its own, so the provider's inspected entry is the only route; a custom harness must do the same.
  6. The token value is redacted by exact match in run output and provider errors; ::add-mask:: is emitted on GitHub Actions; FULLSEND_OPENAI_* are in oidcDenyKeys.

Accepted residual ​

Static placeholders are endpoint-bound at OpenShell 0.0.115: the proxy substitutes the placeholder only on a request to the host, port and path of the profile endpoint that issued it (providers-v2.mdx "Static Credential Endpoint Binding"), so the cross-provider risk ADR 0025 documents — a compromised agent having the gateway resolve the placeholder on another allowed endpoint — no longer applies to this credential. What remains:

  • auth.json is agent-writable during an iteration (pi's config directory is not a permission boundary), and pi re-reads it per request. An agent can therefore change the placeholder pi sends — to nothing that resolves anywhere else — or plant a real key of its own; both are self-sabotage, not a leak of the run's credential. The integrity guard runs at iteration start, before and after .env, not continuously.
  • An iteration starting in the same seconds as a refresh seeds auth.json from its own exec environment; the refresher verifies the file after its re-seed and seeds once more if the iteration's write landed last (one poll interval of exposure at most).
  • The token lifetime is bounded by the GitHub assertion (minutes) and by expires_in (at most 1 h); the provider is run-scoped, carries that expiry and is deleted at run end; the mapping grants api.model.request only.

Consequences ​

  • GPT models on pi are usable via openai/<model-id> with no OpenAI credential inside the sandbox.
  • The runner refreshes the credential for the life of the run: a WIF token is re-exchanged from a fresh GitHub assertion before expires_in (at a margin capped to half the token's lifetime, so a minutes-long token refreshes every couple of minutes) and updated into the run-scoped provider in one call with its new expiry, then waits (up to 90 s; ~20 s measured) for the sandbox to hand new processes the new placeholder and re-seeds pi's auth.json with it (a settle timeout fails the attempt rather than re-seeding the old placeholder); a static key's provider expiry is pushed out on the same schedule and re-seeded the same way, because that update is a new generation as well. When the bounded retries fail, the running pi keeps the generation it holds, which stops resolving when that token expires — the run fails visibly rather than silently outliving its credential.
  • Verified against OpenShell 0.0.115 on a live gateway (2026-08-27), re-verify on every bump. (a) The placeholder in the sandbox environment is a placeholder in the openshell:resolve:env namespace with an opaque revision (v<opaque>_OPENAI_API_KEY) and resolves; (b) the canonical, unrevisioned form (OPENAI_API_KEY in that namespace) returns 500 credential_unavailable for this endpoint-bound credential (crates/openshell-core/src/secrets.rsresolve_placeholder); (c) after provider update, a placeholder issued for the previous generation keeps resolving to the previous value (OpenShell retains up to eight generations, MAX_RETAINED_CREDENTIAL_GENERATIONS; only once a generation ages out does its placeholder fall back to the current credential — eleven quick updates were observed to leave the old value resolvable, the supervisor's ~10 s poll coalescing them into fewer generations), while the sandbox hands new processes a new placeholder within ~20 s (one poll); (d) expiring the credential in place makes every generation fail closed, and an expiry-only update is a new generation too, whose predecessor keeps the expiry it was built with. (c) and (d) are why the file hand-off exists; it also contradicts the 0.0.115 providers-v2 documentation ("the proxy resolves existing placeholders against current credentials … so rotation … take effect without restarting the process"), which describes gateway-managed refresh handles, not static/external credentials. TestPiOpenAIAuthSeed, TestReseedOpenAIAuth_* and TestRefreshOpenAIProvider_ReseedsOnlyOnce… pin the runner side; pi's side — AuthStorage re-reading auth.json when its file revision changes and prepareRequest resolving auth per request — is verified in the pi 0.84.3 source (packages/coding-agent/src/core/auth-storage.ts, packages/ai/src/auth/resolve.ts, model-runtime.ts) and exercised across iteration starts locally, but a rotation inside one running iteration has not been observed live yet: the first WIF run is that check. If it fails, the failure is visible (401 after the old token's expiry, with the refresher's log lines to go on) and the fallback is to shorten iterations below the token lifetime.
  • OpenShell 0.0.110+ resets any model request whose body contains the contiguous placeholder prefix (openshell:resolve:env followed by a colon) — it is treated as credential-bearing traffic that cannot be rewritten. An agent therefore cannot read a file, diff or PR body that spells the prefix out; this repository builds it from two parts in source and tests and never writes it contiguously in docs. Verified in the v0.0.115 source: the guard is a plain substring test on the prefix (crates/openshell-core/src/secrets.rs:44-55contains_raw_reserved_marker, streamed by crates/openshell-supervisor-network/src/l7/rest.rs:1169-1182), it never parses what follows, and it applies to every inspected REST endpoint as soon as the sandbox holds any static provider credential (l7/mod.rs:317-318, l7/relay.rs:842) — so a credential-less endpoint such as Vertex is guarded too once github-ro is attached. Intended fail-closed design (OpenShell PR #2162: a live placeholder must never leave the proxy unresolved); the bare-prefix false positive is the open upstream issue NVIDIA/OpenShell#2904. request_body_credential_rewrite: true is not an opt-out (an unresolvable marker still fails, rest.rs:1698); the only one is allow_uninspected_credentials: true on the model endpoint, which forwards such a body raw while the bearer header is still injected and the method/path rules still apply (verified: a body carrying the prefix, and even the real placeholder string, gets 200; GET /v1/models stays 403). A literal placeholder — a reserved token, not a secret — would then reach the model API. Adopted for the two default model profiles fullsend ships (profiles/fullsend-openai.yaml and profiles/fullsend-vertex-ai.yaml); the fleet's own agents resolve their Vertex profile from fullsend-ai/agents (harness/*.yaml → profiles/fullsend-vertex-ai.yaml), which needs the same flag to protect fullsend's review/code agents, and the upstream fix is NVIDIA/OpenShell#2904.
  • Static credentials are endpoint-bound at 0.0.115: the proxy substitutes a placeholder only at the host, port and path of the profile endpoint that issued it (providers-v2.mdx "Static Credential Endpoint Binding"). The residual this ADR inherited from ADR 0025 — a compromised agent resolving the placeholder against another allowed host — is closed for this credential.
  • A harness without policy: fails the egress preflight on the base image (its default policy allows api.openai.com:443 as a raw tunnel for /usr/bin/node); the fleet's policies/base.yaml is the documented answer for custom and local harnesses.
  • The three identifiers live in the committed inference.openai block of .fullsend/config.yaml, written by fullsend github setup --openai-* like the Vertex project and provider; they are not secrets (a token is issued only to a caller whose GitHub OIDC claims match the mapping, and pull-request events read the config from the base branch, ADR 0033). Within config.yaml the three resolve through the layers field by field, so a base preset can carry the organization's audience and identity provider and each repository its service account. The reusable workflows also pass the FULLSEND_OPENAI_* repository variables into the runner environment for installations that prefer not to commit them; when any is set they replace the resolved block, never merge with it. On a machine without a GitHub OIDC endpoint a set OPENAI_API_KEY wins over the block, so a developer's local run of a repository that committed it still works.
  • Live end-to-end verification is gated on external access and run by a maintainer after merge.
  • ADR 0025 — provider-based credential delivery (tier definitions)
  • ADR 0073 — oidcDenyKeys (#5832)
  • #6532 — GPT / Azure OpenAI / Bedrock providers for pi
  • #6464 — pi runtime tracker
  • #1952 — Anthropic WIF sibling design
  • ADR 0095 — mapping scope: repository-only by default (#6782)
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