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We are currently stuck on CAS 3.0, but modern versions of CAS are up to version 7 or so. Simply upgrading it may support the existing applications while opening up significant authorization possibilities. Research into this was conducted last year by Richard Falardeau, but I don't have the output of that research on-hand. which I think mostly wound up in the following repo:
https://open-bitbucket.nrao.edu/projects/SSA/repos/user-portal/browse
This should feed the first step of both implementation plans, determining the successor technology.