Description

aicr bundle --attest currently supports exactly two OIDC paths:

1. Ambient via GitHub Actions env vars (ACTIONS_ID_TOKEN_REQUEST_URL
   • ACTIONS_ID_TOKEN_REQUEST_TOKEN) — CI only.
2. Interactive browser via oauthflow.DefaultIDTokenGetter — prints
   a pasteable URL but uses a redirect-callback on an ephemeral
   localhost:<random-port>. After the user logs in on a laptop, the
   OIDC provider tries to hit localhost:<port> on the laptop — never
   on the headless box where aicr runs.

No COSIGN_IDENTITY_TOKEN / --identity-token flag, no device-code
flow, no cloud workload-identity providers.

Impact

Medium — blocks --attest on headless hosts (bastions, remote build
boxes, air-gapped runners). Workarounds exist (SSH port-forward the
random callback; run on the laptop) but all are gymnastics.

Reproduction

# On a headless box (no DISPLAY, no browser)
ssh some-headless-host
unset DISPLAY
aicr bundle --recipe recipe.yaml --output ./b --attest
# Hangs at the OAuth callback (sigstore InteractiveOIDCTimeout = 5min).
# No path forward without leaving the box.

Where

• pkg/cli/bundle.go:510 — selectAttester
• pkg/bundler/attestation/oidc.go
• sigstore device-code helper already vendored:
  vendor/github.com/sigstore/sigstore/pkg/oauthflow/interactive.go:134
  (NewDeviceFlowTokenGetterForIssuer)

Proposed Fix

Pick one or both (both are non-breaking):

A. Expose sigstore's device-code flow behind a flag/env var.
Lowest friction for new users:

// selectAttester gains a new branch before the interactive fallback:
if useDeviceFlow() {
    oidcToken, err := attestation.FetchDeviceCodeOIDCToken(ctx)
    ...
}

User sees Go to URL ... Enter code XXXX-XXXX — fully headless.

B. Accept a pre-fetched token via COSIGN_IDENTITY_TOKEN /
--identity-token. Simpler to plumb; matches cosign upstream ergonomics.

Scope

Dedicated PR. Not stable-blocking unless scope allows — workarounds
exist. Add tests for both code paths in
pkg/bundler/attestation/oidc_test.go.