make set_spapprole work in a VBA context
SQL Server (see https://docs.microsoft.com/en-us/sql/relational-databases/system-stored-procedures/sp-setapprole-transact-sql?view=sql-server-2017) has a great security feature to allow an app to assume a security role when connected to the server. This doesn't work from Access VBA. This leaves us having to give permissions to data that users can subvert. Whilst this can be mitigated, if Access could connect using a user account with no permissions, and switch to an app role with the right permissions security would be wonderful. SetAppRole is particular pleasant in that in the context we still know the original user who started the app.