config.c: Add exec support to OIDCClientSecret

[sealor]

I noticed that there is an "exec" support available for OIDCCryptoPassphrase and OIDCClientTokenEndpointKeyPassword. I need a similar feature for OIDCClientSecret to retrieve the secret from a secured location.

So, I propose adding this also for OIDCClientSecret.

The current implementation does not allow passphrases, passwords and secrets starting with "exec:". Perhabs, this could be fixed by adding new configuration parameters like OIDCCryptoPassphraseExec, OIDCClientTokenEndpointKeyPasswordExec and OIDCClientSecretExec. What do you think about this approach?

[zandbelt]

thank you for the contribution! I'd prefer to keep things as they are - to avoid cluttering the configuration file with even more primitives - and take the risk that you mention

[zandbelt]

please add an entry to the ChangeLog and add yourself to the AUTHORS file as well, thanks

[sealor]

@zandbelt
Thank you for your fast feedback! I added an entry to ChangeLog and AUTHORS as mentioned.