Motivation

• The GetSandboxProviderEnvironment RPC previously returned provider credential key/value pairs for any caller-supplied sandbox_id with no caller identity binding, allowing unauthenticated clients to exfiltrate secrets.
• The intent of the change is to ensure credential material can only be retrieved by the sandbox that owns the requested sandbox_id by binding the request to the caller identity.

Description

• Add a shared metadata key constant HEADER_SANDBOX_ID ("x-sandbox-id") to bind requests to a sandbox identity.
• Implement authorize_sandbox_request(request, sandbox_id) which validates presence of the x-sandbox-id metadata and enforces it equals the requested sandbox_id.
• Enforce the authorization check at the start of get_sandbox_provider_environment so no sandbox or provider lookups occur for unauthorized callers.
• Add focused unit tests exercising authorize_sandbox_request for matching metadata, missing metadata, and mismatched sandbox_id cases and expose the helper in the test import list.

Testing

• Ran cargo test -p openshell-server authorize_sandbox_request -- --nocapture and the three new authorization tests passed (3 passed; 0 failed).
• Ran cargo fmt --all to format changes (succeeded in this environment).
• Attempted mise run pre-commit but it failed in this environment due to remote tool resolution / trust restrictions (not a code failure).

Codex Task