While I was creating an openclipart plugin for the Godot Engine, I have created an HTTP class for downloading the data and images. Godot has built-in support for HTTP get/post data. An example on how to use the HTTPClient is already available on godot github wiki page.
The plugin loads multiple images simultaneously so I was in need of creating a class for that. Also there are multiple things are loaded, there is a chance of blocking the UI. Here comes multi-threading to the rescue. Godot wiki also has an example for background resource loading in another thread.