Capture JWT claims

[Munken]

Case:
I want to extract a claim from the JWT token in the Authorization header from the http request and add it to http.server.duration.

I found the header capture, but I don't want to capture the raw authorization header.

I had a look at DemoServlet3Instrumentation and came up with the following. However, the histogram construction seems closed for extension?

@Advice.OnMethodEnter(suppress = Throwable.class)
    public static void onEnter(@Advice.Argument(value = 0) ServletRequest response) {
      if (!(response instanceof HttpServletRequest)) {
        return;
      }

      HttpServletRequest httpServletResponse = (HttpServletRequest) response;
      String header = httpServletResponse.getHeader("x-my-custom-header");
      if (header != null) {
        Java8BytecodeBridge.currentSpan().setAttribute("x-my-custom-header", header);
      }
    }

Is this the correct way?

[laurit]

Is this the correct way?

This won't work. Metric attributes aren't read from the span but rather from what is added to the span by our instrumentation.

[Munken]

Is there a way to do it?

Looks like one would have to add an Attribute Extractor to the builder?

opentelemetry-java-instrumentation/instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/builder/internal/DefaultHttpServerInstrumenterBuilder.java

Line 102 in e02076c

public DefaultHttpServerInstrumenterBuilder<REQUEST, RESPONSE> addAttributesExtractor(

[laurit]

Currently there isn't a good way to do this. Probably your best option is to copy the server instrumentation you use, modify it to suite your needs and disable the original instrumentation. #13917 may provide an easier way for this.