love-gamejolt-api
This is the lua script I've used to upload high-scores to GameJolt in the past. It isn't very featureful, since all I needed was to upload a high-score. Hopefully it will help you get started using the GameJolt API through LOVE2D!
Example
local gj = GameJolt(game_id, private_key)
gj.connect_user(username, token)
gj.add_score("100 points", 100)Check out the example app!