Fwiw.. I have a "normal" private git server over SSH, but for public projects, it copies merges into blessed branches to public, read-only repos accessible via HTTPS. Here's an example:

https://www.bi6.us/GI/B/

I sort of punted on receiving patches and merge requests because most of the projects I'm distributing in this way aren't really open source, but "published source" and there's a small community of people who use them. The people who use the public, read-only repos know how to generate patches and distribute them via email or (in one case) uploading them to an S3 bucket.

Anyway... your mileage may vary, but it's worked reasonably well for a small community. Not sure I would recommend it for a huge open source project.