OIDC client_secret overwritten with placeholders on settings save

[ErikMichelson]

Version:

• listmonk: v4.0.1 in docker with postgres
• Docker: 27.3.1
• OS: Debian 12

Description of the bug and steps to reproduce:

I have configured OIDC. It worked as expected. Some days later I changed another setting, which resulted in me not being able to log in via OIDC anymore with an error stating that the client_secret would be wrong.

Some investigation in the database showed me that the OIDC client_secret seems to be overwritten with placeholder characters on further settings changes.

To reproduce:

1. Configure OIDC with a client_secret
2. Verify that the database contains the right secret: SELECT value->>'client_secret' AS value FROM settings WHERE key = 'security.oidc';
3. Change another setting and save the settings again
4. Run the SQL query to extract the client_secret again: See that it changed to placeholder characters

[ErikMichelson]

Oh, I just looked through the recent development and found this promising commit: https://github.com/knadh/listmonk/commit/5abf004655ad457e0fe319ce18487c73957b36b3

I guess this problem should be resolved with it, and I am waiting happily for the next release. :)