If you want to post parameter in okhttp as body content which can be encrypted string with content-type as "application/x-www-form-urlencoded" you can first use URLEncoder to encode the data and then use :
final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("application/x-www-form-urlencoded");
okhttp3.Request request = new okhttp3.Request.Builder()
.url(urlOfServer)
.post(RequestBody.create(MEDIA_TYPE_MARKDOWN, yourBodyDataToPostOnserver))
.build();
you can add header according to your requirement.