code: private String token(final String home, final String code)
          throws IOException {
          final String response = this.request
              .uri()
              .set(
                  URI.create(
                      new Href(PsFacebook.ACCESS_TOKEN_URL)
                          .with(PsFacebook.CLIENT_ID, this.app)
                          .with("redirect_uri", home)
                          .with(PsFacebook.CLIENT_SECRET, this.key)
                          .with(PsFacebook.CODE, code)
                          .toString()
                  )
              )
              .back()
              .fetch()
              .as(RestResponse.class)
              .assertStatus(HttpURLConnection.HTTP_OK).body();
          final String[] sectors = response.split("&");
          for (final String sector : sectors) {
              final String[] pair = sector.split("=");
              if (pair.length != 2) {
                  throw new IllegalArgumentException(
                      String.format("Invalid response: '%s'", response)
                  );
              }
              if ("access_token".equals(pair[0])) {
                  return pair[1];
              }
          }
          throw new IllegalArgumentException(
              String.format(
                  "Access token not found in response: '%s'",
                  response
              )
          );
      }
docs: Retrieve Facebook access token.
  @param home Home of this page
  @param code Facebook "authorization code"
  @return The token
  @throws IOException If failed