Add radiustimeout parameter for RADIUS HBA

Hello everyone,

I’d like to submit the attached patch for feedback from the PostgreSQL community and potential future inclusion in the codebase. The patch adds a new parameter to the RADIUS authentication method named “radiustimeout”, allowing the database administrator to configure the timeout in seconds to wait for responses from a configured RADIUS server. Until now, this has been hardcoded to three seconds by the RADIUS_TIMEOUT define in auth.c. While this is usually sufficient for typical RADIUS server configurations, there are some more unusual configurations where a higher timeout is required. Examples include:
- Authenticating against a RADIUS server over a high latency link
- Authenticating against a RADIUS server that is performing additional out-of-band authentication

The latter case is applicable to a server I admin and spurred the development of this patch. We implemented multi-factor authentication for user access to a sensitive database via a RADIUS server implementation which performs the standard username & password verification, and if it succeeds, subsequently performs a second factor of authentication via a configured mobile app. The RADIUS response confirming successful authentication is only returned after both authentication factors have completed. In our deployment, a timeout of 60 seconds seems to work well, but certainly three seconds is not at all workable.

Thanks in advance for any and all feedback.

Kind regards,
-SDL