Spring WebClient set Bearer auth token in header

Question

Following scenario:

I have two Microservices A and B. Service A is a Bearer client that has an open api and receives requests from clients that have to be authorized by keycloak. Now I want to send an authorized Request from Service A to Service B, which is also a bearer client.

I thought about adding the functionality as a filter function during the webclient builder process like

@Bean
WebClient webClient() {
    return WebClient.builder()
            .filter(authHeader())
            .build();
}

private ExchangeFilterFunction authHeader(String token) {
    return (request, next) -> next.exchange(ClientRequest.from(request).headers((headers) -> {
        headers.setBearerAuth(token);
    }).build());
}

This is an example I found in another question. It seems to to be the right way to me but can I provide the "String token" parameter at that stage of configuration?

I'm just switching from RestTemplate to WebClient, so sorry I this is a dump question.

EDIT: I am able to set the header manually while building a new WebClient.

return WebClient.builder()
        .defaultHeader("Authorization", "Bearer "+ context.getTokenString())
        .build();

As I know from the RestTemplate, it can be used as a Singleton. There also exists a KeyCloakRestTemplate which injects the header automatically.

WebClient is immutable, so when I inject it, I can't just use it and add the header afterwards. In addition, I can't set this header on startup as I have to wait for a request to take the bearer header and pass it in. So I guess there is not other way than doing it this way?

Answer 1

Or simply set it during the process of sending:

webClient.get()
    .uri(url)
    .headers(h -> h.setBearerAuth(token))
    .retrieve();