@Override
    public Request apply(RequestTemplate input) {
      if (input.url().indexOf("http") != 0) {
        throw new UnsupportedOperationException(
            "Request with non-absolute URL not supported with empty target");
      }
      return input.request();
    }
Targets a template to this target, adding the {@link #url() base url} and any target-specific
headers or query parameters. <br>
<br>
For example: <br>

<pre>
public Request apply(RequestTemplate input) {
  input.insert(0, url());
  input.replaceHeader(&quot;X-Auth&quot;, currentToken);
  return input.asRequest();
}
</pre>

<br>
<br>
<br>
<b>relationship to JAXRS 2.0</b><br>
<br>
This call is similar to {@code javax.ws.rs.client.WebTarget.request()}, except that we expect
transient, but necessary decoration to be applied on invocation.
core/src/main/java/feign/Target.java