I am trying to use with GitHub Enterprise, however it keeps asking for a username and password. We are using the CAS backend.
I don't know what a CAS backend is. GitHub has two different types of authentication:
hub uses GitHub API, so it needs to exchange your username/password for OAuth keys. This has nothing to do with git protocol over SSH, and SSH keys can't help here.
I suspect that whatever CAS is, it means you don't have a regular GH Enterprise username/password that you can pass on the command-line. Not sure how to work around this
Here's a person who had the same issue and solved it manually #293 (comment)
I understand that this is hackish and confusing. I'll look into how to support the web-based OAuth flow in case there's no username/password. However, in the meantime you're on your own