Unrecognized configuration parameter when using set_config(text, text, boolean) in CTE

I’m trying to implement a simple ABAC system using row level security, with main policy defined as following:

CREATE policy resource_access ON resource
    org_id::varchar = current_setting('', true)
    acl_read && regexp_split_to_array(current_setting('scope.acl'), ',')::varchar[]

Issuing queries akin to:

  acl AS (SELECT set_config('scope.acl', 'ACL', true) "__acl"), 
  result AS ( ... )
SELECT * FROM acl, result

With the main reason to use WITH is to avoid multiple statements when queries are later PREPAREd and EXECUTEd by the Postgres driver I’m using.

The result in example above can contain any arbitrary queries required by the application. To ensure that set_config is executed in the query, it’s also added to the final SELECT.

However, I still do consistently encounter the following error:

QueryFailedError: unrecognized configuration parameter "scope.acl"

Which appears to be caused by executing the subquery from WITH in isolation from the result query.

So the main questions are:

  • Is there any elegant way to ensure running set_config before the main query (the one in result) is executed?
  • Is there any better way to construct queries for the application side, to avoid using WITH, but keeping them as a single SQL statement?

Thank you!

Database Administrators Asked by Ivan C. on December 28, 2020

1 Answers

One Answer

We've ended up using the JOINs over CTEs, which implicitly applies the expected order, and queries looking like:

      acl AS (SELECT set_config('scope.acl', 'VALUE', TRUE) "__acl"),
      result AS (${query})
    SELECT * FROM bypass FULL OUTER JOIN result ON 1 = 1

In which case, acl CTE runs before the result and ensures that RLS could pick up a correct configuration.

Whilst it might very well be sub-optimal for a larger scale table, it worked perfectly for our scale (10k-100k rows) with no noticeable performance degradation compared to using CTEs without the resulting FULL OUTER JOIN. More importantly, our correctness tests haven't highlighted any deviations from the expected order, despite this behavior (of result running after acl in CTEs block) is implicit.

Answered by Ivan Cherepanov on December 28, 2020

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