Signature invalid when I try to authenticate the user?

It's simple. You have to get such values from gamejolt pages:

• Your Game Id

• Your Game Private Key

• User Name

• User Token

First, create your call URL. So for authentication it'll be something like:
URL="https://api.gamejolt.com/api/game/v1_2/users/auth/?game_id=GAMEID&user_token=USERTOKEN&username=USERNAME" (for GAMEID/USERTOKEN/USERNAME you have to put correct values.

Than take your game private key and append it to your URL.
URL_WITH_KEY=URL + GAME_PRIVATE_KEY

Now calculate hash (MD5 or SHA1)
SIGNATURE=hash(URL_WITH_KEY)

And now the url with signature will be:
FINAL_URL=URL + "&signature=" + SIGNATURE

You may also look at may code of plugin for godot: https://github.com/rojekabc/-godot-gj-api/blob/master/main.gd . It's in the function _compose_url at line 204

Thank you!

I'm just testing stuff out. What is a hash, why do you calculate it, how do you calculate it, what is MD5, what is SHA1, what do these two terms mean, how is each format written and punctuated, where can one be entered as part of a URL-based-request, and may I please have an example of a pretend-URL-request that could have its values swapped out with my game's information and entered into my browser for the testing of my own game's trophy-system?

In other words, the hash, its proper-formatting, and its position in the URL; are the only three parts of the signature that I apparently-don't understand, as all my attempts lead to it saying that the signature is invalid.

Thank you so very much!