Why would github application ask write access to my private repo?

Question

I'm signing up a website with my github account. But why would github allow application gain access to my private repo?

What I expect is that github should allow me to control which access I want to grant to that application.

This application will be able to read and write all public and private repository data. This includes the following:

• Code
• Issues
• Pull
• requests
• Wikis
• Settings
• Webhooks and services
• Deploy keys

Answer 1

Github's permissions are, unfortunately, not all that granular.

They're listed here: https://docs.github.com/en/apps/oauth-apps/building-oauth-apps/scopes-for-oauth-apps

The site is presumably requesting the repo permission. It'd be nice if Github let you pick and choose which repositories to allow a third-party application access to, but it's currently all-or-nothing.

The site may or may not have a legitimate need for that permission (a CI service might need access to a private repo, for example). We can't answer that part for you - you'll have to decide for yourself if the login is worth the risk.