Sharing private git repo via access link

This is:

• not possible with GitHub (you would need to add a user as a collaborator of a private repo)
• discussed, but not yet implemented on GitLab: issue 20549: "Share private project via URL" (since April 2016)

So you might need to use a third-party option (like the ones you mention, or GitFront -- from Serbia -- mentioned below,) to package/publish (and update) your repository, for any user to access it with a link. For example, publish it as a bundle (one file).

You can use GitFront to share private git repositories.

It is a web application that allows you to import a repository and create a read-only version of it, which is sharable via link. The person receiving the link doesn't need to have an account to view the repository.

Disclosure: Affiliated with GitFront.