Valid characters for PostgreSQL session parameters

Question

Where can I find the list of characters which are valid for PostgreSQL configuration parameter names? By trial and error I found that '.' and '_' are valid, but ':' isn't. Quoting doesn't seem to help.

set claims.custom_id to asdf; -- accepted
set "claims.custom:id" to asdf; -- invalid configuration parameter name

The PostgreSQL docs don't seem to cover this point - https://www.postgresql.org/docs/current/config-setting.html

Answer 1

This is a breaking change introduced in PostgreSQL 14: Require custom server parameter names to use only characters that are valid in unquoted SQL identifiers (Tom Lane)

https://www.postgresql.org/docs/14/release-14.html

The rationale is given here:

https://www.postgresql.org/docs/14/runtime-config-custom.html