CVE-2026-101916: @grpc/grpc-js: In certain configurations, getAuthContext can return unauthorized certificates as though they were authorized

### Impact When server credentials are created with the `requireClientCertificate` option set to `false`, `getAuthContext` does not distinguish between authorized and unauthorized certificates in its return value. This can create improper authentication vulnerabilities for `@grpc/grpc-js` users who use the result of `getAuthContext` for authentication. In particular, `@grpc/grpc-js-xds` can both set the `requireClientCertificate` option to `false` and use the return value of `getAuthContext` for RBAC authentication in some configurations. ### Patches This vulenrability is fixed in 1.13.6 and 1.14.5. ### Workarounds `@grpc/grpc-js` users using `getAuthContext` this way can avoid this problem by setting `requireClientCertificate` to `true`. `@grpc/grpc-js-xds` users using RBAC can avoid this by setting the `require_client_certificate` field to `true` in the DownstreamTlsContext in the xDS configuration.