I did some research, these are some of the libraries
2. This is is built for automatic updates for private and commercial plugins that are not found in the general wordpress repository but can be used outside wordpress.
Another similar one here https://github.com/YahnisElsts/plugin-update-checker
There are very good articles on exactly how wordpress automatic updates works
1.How wp auto updates works
2.wordpress automatic updates
3.Explaining wp auto updates