On Mon, August 20, 2007 19:52, Andrew Dunstan wrote:

> I'd rather see an HBA fallback mechanism, which I suspect might overcome
> most of the  problems being encountered here.

I implemented a form of that once, so on local connections you could do
ident mapping with fallback to PAM or some other password authentication. 
That seemed useful, e.g. for granting non-interactive access to a program
running under a dedicated user and requiring a password from everyone
else.  The implementation also allowed for a bit more flexibility in the
auth mechanism.

The main objections I recall were:

1. The protocol doesn't allow for multiple authentication prompts.  My own
proposal didn't have that problem since it only introduced an "optional
ident" authentication that continued looking for a matching rule if the
current user name was not in the given map, but it's a problem for more
general approaches.

2. For real, fully generalized fallback, you'd also need to overhaul the
HBA config file format completely.

3. It was considered unsafe to add even the most limited of fallback
options, because the HBA config is designed to pick just one auth
mechanism for any connection attempt, based on only the first three
columns of the config file.  An admin who didn't understand the new auth
mechanism could use it to write an unsafe HBA configuration, provided it
also broke the existing "go from specific-permissive to
general-restrictive" design guideline.

Personally I think it'd take some careful aim to shoot yourself in the
foot like that, but IIRC it was enough for an "I don't like it" vote.


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