Outgoing request filter from Rest-Application?

Question

Java

Hello, I don’t know how to do it or where to look ...

There is a Rest-service - we call another service from it by url or using org.apache.cxf.jaxrs.client.WebClient-
How can I check the header in such an outgoing request?
We need some kind of filter or listener that looks at all outgoing requests. The normal filter only works when the client sends a request.

Thank you!