code: public static Condition withHeader(final String key) {
          return new Condition(input -> {
              for (String k : input.getHeaders().keySet()) {
                  if (k.equalsIgnoreCase(key)) return true;
              }
              return false;
          });
      }
docs: With header present.
  Header key is case insensitive. More information <a href="http://stackoverflow.com/questions/5258977/are-http-headers-case-sensitive">here</a>.