A user who doesn't have access to a table should also not be able to modify Phoenix Metadata. Currently, every user required to have a write permission to SYSTEM tables which is a security concern as they can create/alter/drop/corrupt meta data of any other table without proper access to the corresponding physical tables.
Devaraj Das recommended a solution as below.
1. A coprocessor endpoint would be implemented and all write accesses to the catalog table would have to necessarily go through that. The 'hbase' user would own that table. Today, there is MetaDataEndpointImpl that's run on the RS where the catalog is hosted, and that could be enhanced to serve the purpose we need.
2. The regionserver hosting the catalog table would do the needful for all catalog updates - creating the mutations as needed, that is.
3. The coprocessor endpoint could use Ranger to do necessary authorization checks before updating the catalog table. So for example, if a user doesn't have authorization to create a table in a certain namespace, or update the schema, etc., it can reject such requests outright. Only after successful validations, does it perform the operations (physical operations to do with creating the table, and updating the catalog table with the necessary mutations).
4. In essence, the code that implements dealing with DDLs, would be hosted in the catalog table endpoint. The client code would be really thin, and it would just invoke the endpoint with the necessary info. The additional thing that needs to be done in the endpoint is the validation of authorization to prevent unauthorized users from making changes to someone else's tables/schemas/etc. For example, one should be able to create a view on a table if he has read access on the base table. That mutation on the catalog table would be permitted. For changing the schema (adding a new column for example), the said user would need write permission on the table... etc etc.
Thanks Josh Elser for the write-up.