I had similar issue but in python , godot and firebase. I never used c or curl http but this answer might be helpfull for you, I hope. Well, the solution wasn't secure and effective but for a school program it might be ok. here is what I did:

A few days ago, I was trying to figure out multiplayer on godot using firestore(was a bad idea i know). I needed to somehow pass all the client id's/document id's into the client game to make it functional. but using the godot firebase addon wasn't easy for me. thus, I created a python file to extract all the user from the firestore database(I know not secure and not what you want, but it is the strategy is similar) and save it into a users Array under "user_list@@gsjsXQDjs" document_id and extract it easily on client game. I had made a tempory Social media: a twitter like app for my school friends using this strategy. dough I know I have look for security features in future which is another headache.

I know you are doing a different task but the strategy may help you if you want a quick application for your school and don't care about security for now.