Vertex authorization error is not reported.

[damo]

If I use an invalid OAuth2 token to connect to Vertex, the response has code 401 and the response body looks like this:

[{
  "error": {
    "code": 401,
    "message": "Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.",
    "status": "UNAUTHENTICATED",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.ErrorInfo",
        "reason": "ACCESS_TOKEN_TYPE_UNSUPPORTED",
        "metadata": {
          "method": "google.cloud.aiplatform.v1.PredictionService.StreamRawPredict",
          "service": "aiplatform.googleapis.com"
        }
      }
    ]
  }
}
]

That all seems reasonable, but why does the ErrorHandler not throw an UnauthorizedException? Or is the exception being swallowed up somewhere?