Data Sources, vary user credentials based by current user

It seems to me that Data Sources are only available for the administrator who configures it. The user name and password set on for example Postgres, Sql Server and Json data sources is global for all users. I think it would be benificial to be able to override the username and password per datasource. For example in Postgres row level security exists and can be used with policies on tables to filter data. By allowing the username to vary with each user it is possible to use different accounts and therefor retrieve filtered data from Postgres for the specific user permissions.
Please correct me if I am mistaken that the username/password is global for a data source once setup.

This is commonly known as credential passthrough. Would love to see this come to Redash. This will be part of the discussion of coming features after the V10 release in a few weeks.