forcing a literal value in a column

Hello all,

in my audit trail tables I want two columns to _always_ be
CURRENT_USER/CURRENT_TIMESTAMP.

I am currently doing this:
...
modified_by name not null default CURRENT_USER check(modified_by=CURRENT_USER),
...
(respective for CURRENT_TIMESTAMP)

I know this can also be achieved with a trigger on insert/update.
However, I'd like to know what is the "PostgreSQL way" of
doing this ? Do I achieve what I want with my above solution ?
It seems to work but feels clunky.

I am sure this has been discussed before on the mailing lists
but despite my search I have not been able to locate the
threads. Please point me to the keywords I need to use for the
search to succeed.

Thanks,
Karsten
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