I am building a static application aiming for zero-costs apart from static content distribution, and for potential user interaction would like to embed a service which allows versioned edits to embedded content. Ideally, I would have liked to have used github, for instance to submit content directly from specific pages, but github uses OAuth 2.0 which would require some kind of backend process. Google and FB have web logins but the types of content embedding they provide aren't particularly useful (unless I am mistaken).
My question is what other options are out there that might provide git-based embedded content. Ideally not bloatware.
Just to stress that I am not interested in any kind of service like Cognito or Firebase or oauth.io.