Hello Ethan,
For getting the accounts, use your choice of GetUserAccountList. The result should contain the CIF.
For getting the User based on an internal CIF you can use the User db object. https://docs.q2developer.com/api_references/q2_sdk/db/db_objects/user.html?highlight=getuser#q2_sdk.hq.db.user.User.get
Hope this helps,
Trey Teter
Software Engineer