code: public Identity identity() throws IOException {
          final Iterator<String> headers =
              new RqHeaders.Base(this).header(this.header).iterator();
          final Identity user;
          if (headers.hasNext()) {
              user = new CcPlain().decode(
                  new Utf8String(headers.next()).asBytes()
              );
          } else {
              user = Identity.ANONYMOUS;
          }
          return user;
      }
docs: Authenticated user.
  @return User identity
  @throws IOException If fails