Spring Allow HttpHeaders invocation on MockHttpServletRequest and MockHttpServletRequestBuilder

It's nice that WebClient and RestClient provides access to the rich HttpHeaders object for setting things like HTTP Basic.

WebClient.create().get()
    .uri("/")
    .headers(h -> h.setBasicAuth("user", "password"))
        // ...

It would be nice if MockHttpServletRequest and MockHttpServletRequestBuilder exposed a method that allowed users to leverage HttpHeaders in a similar way as illustrated above.

NOTE: setHeaders(HttpHeaders) is not desirable because it requires setting all of the headers vs updating the existing HttpHeaders.