Ask HN: Where to allow users to save their data?

I'm working on a quick personal project (a tool) that others I know would like to use. Currently, I have the web app set up to save state to localstorage, which is not ideal. I'd like to allow users to login with a third-party integration to save the data they create with the app. Does anyone know of any APIs or platforms that could be accessed securely via a frontend fetch?