GHSA-5mq7-rwhj-4fh9

### Summary

When Steeltoe's certificate-based authorization (`UseCertificateAuthorization`) is configured, the default configuration of the middleware relies on the `X-Client-Cert` HTTP header to identify the client certificate, without verifying private-key possession. This header is not stripped by common Cloud Foundry routers (like Gorouter or Envoy) on inbound requests.

### Impact

An attacker who obtains the public certificate of an application instance in the target organization or space can spoof the `X-Client-Cert` header. This allows the attacker to bypass `SameOrg` and `SameSpace` authorization policies, granting unauthorized access to protected endpoints for the duration of the certificate's validity period.

### Affected configuration

- The application uses `AddOrgAndSpacePolicies()` and `UseCertificateAuthorization()` for inter-service authorization. - Inbound requests are not restricted to a known trusted proxy source IP. - The application's endpoints are network-accessible to the attacker (e.g., exposed to the internet via a public Cloud Foundry route, or the attacker has access to the internal Cloud Foundry network).

### Mitigations

If an immediate upgrade to a patched version is not possible:

- Restrict `UseCertificateForwarding` to trusted proxy source IPs using `ForwardedHeadersOptions.KnownProxies` and `KnownNetworks`. - Change the forwarding header to `X-Forwarded-Client-Cert` so that Cloud Foundry Gorouter and Envoy header stripping mechanisms apply to inbound untrusted requests. - Add a secondary authorization layer (e.g., a shared secret or mutual TLS at the proxy layer) for sensitive endpoints. - Ensure the application is not bound to a public route unless explicitly required. Use Cloud Foundry internal routes (e.g., `.apps.internal`) and container-to-container network policies to strictly limit network access to intended internal clients.