code: private String token(final String code) throws IOException {
          return new JdkRequest(
              new Href(this.gauth).path("o").path("oauth2").path("token")
                  .toString()
          ).body()
              .formParam("client_id", this.app)
              .formParam("redirect_uri", this.redir)
              .formParam("client_secret", this.key)
              .formParam("grant_type", "authorization_code")
              .formParam(PsGoogle.CODE, code)
              .back()
              .header("Content-Type", "application/x-www-form-urlencoded")
              .method(com.jcabi.http.Request.POST)
              .fetch().as(RestResponse.class)
              .assertStatus(HttpURLConnection.HTTP_OK)
              .as(JsonResponse.class).json()
              .readObject()
              .getString(PsGoogle.ACCESS_TOKEN);
      }
docs: Retrieve Google access token.
  @param code Google "authorization code"
  @return The token
  @throws IOException If failed