Option to pass through external Authorization headers without replacement

Problem Statement

Problem

The supervisor's credential proxy intercepts the Authorization header on incoming requests and attempts to parse it as an OpenShell gateway session token. When an external JWT (e.g., from Auth0, Keycloak, or any OIDC provider) arrives in the Authorization header, the supervisor returns 500 "invalid token: token is malformed".

This prevents using standard bearer token authentication for agents that are exposed as API services to external clients.

Current Behavior

1. External client sends: Authorization: Bearer
2. Supervisor intercepts the header
3. Supervisor tries to parse it as an OpenShell session token
4. Parsing fails → 500 Internal Server Error

Proposed Design

Desired Behavior
Option A: Configurable header behavior — allow the sandbox to declare that the supervisor should not intercept Authorization headers (pass-through mode):

spec:
  supervisor:
    credentials:
      passthroughInboundAuth: true  # Don't intercept incoming Authorization headers

Option B: Graceful fallback — if the token is not a valid OpenShell session token, pass it through unchanged instead of erroring.

Option C: Separate header — use a different header for OpenShell credentials (e.g., X-OpenShell-Token) so Authorization is always available for the agent's own use.

Alternatives Considered

Use Case

Deploying agents as long-running API services where external clients authenticate with JWTs from an enterprise identity provider (Auth0, Keycloak, Okta). The agent needs to receive the user's identity for personalization, audit, or downstream delegation (On-Behalf-Of flows).

Workaround

We use an Istio ext_authz filter at the sidecar level that:

1. Validates the external JWT
2. Strips the Authorization header (so supervisor doesn't see it)
3. Injects X-End-User-ID for identity propagation
4. Injects X-Original-Token for downstream OBO flows

This works but loses the ability to have the agent itself validate/inspect the original token.

Agent Investigation

No response

Checklist

• I've reviewed existing issues and the architecture docs
• This is a design proposal, not a "please build this" request

Start by tracing the supervisor's credential proxy and its handling of inbound Authorization headers; the issue does not name specific files or tests. Determine which proposed behavior is accepted, then verify that external bearer tokens reach the agent unchanged without breaking OpenShell session credentials.