Best way to access client's Github repo as an organization with multiple devs

Question

Together with some colleagues I'll be making changes to a client's codebase. Normally when working on projects we create a repo for our organization on Github and setup permissions on a per-user basis.

But for this project we will have to work with a repo owned by the client. I was hoping we could have them add our organization as a collaborator and we'd be all set, but it seems you can't add a organization, only regular users.

Asking the client to add every dev as a separate collaborator on the client's repo would be extremely messy. What would be a better way of allowing our multiple devs access to a remote repo?

A last resort might be to have them share it with a single dev who can fork the project and allows the rest access to this fork, creating pull requests on the main repo as we go, but direct access for everyone would be preferable as the devs involved will change over time.

edit: This post was commented as a possible solution and while the question is very similar (though 4 years old) no real solution was given.

Answer 1

When the client has GitHub enterprise and an Identity Provider configured with SAML and SCIM support, they can add your team as a guest in their IdP and sync into GitHub. That way they could federate in your team from another organization in the IdP.

If that's not an option, they could make you/a few team members part of the admin group of the repository.

Forking may be an option too, but forking private repos across organizations with pull requests and all isn't supported.