Which of the following locations can Terraform use as a private source for modules?

Terraform can indeed use an internally hosted Source Control Manager (SCM) platform as a private source for modules. This is particularly valuable for organizations that want to maintain strict control over their module sources and prefer to use their own infrastructure rather than public repositories.

By using an internally hosted SCM platform, teams can collaborate on modules securely and ensure that access is restricted to authorized personnel only. This promotes better governance and compliance with internal policies regarding code confidentiality and intellectual property.

While public repositories on GitHub and private GitHub repositories are valid sources for modules, they don't specifically represent a private solution if you're highlighting the need to control access and maintain confidentiality. External cloud storage, depending on its configuration, may not provide the same level of detailed version control and collaboration features that an SCM can offer, which is another reason why the internally hosted SCM is an ideal choice for a private module source.