Currently we are pushing Extension configuration to Envoy as a Struct type. Although it's documented that it should be supported, when the extension retrieves the config via proxy_get_configuration() API call, it receives binary data. It's not clear if this is a bug or not.

The way to go - upstream has decided this way too - is to push the configuration as string.

Going from this:

configuration:
  "@type": google.protobuf.Struct
  key: value
  nested: 
    foo: bar

To this:

configuration: |
    { 
      "key": "value",
      "nested": {
          "foo" : "bar"
      }
    }

Then extensions will receive a string as a result of proxy_get_configuration() and can parse it as JSON as needed.