Re: [PoC] Let libpq reject unexpected authentication requests

[Peter Eisentraut]

I'm wondering about making the list of things you can specify in 
require_auth less confusing and future proof.

For example, before long someone is going to try putting "ldap" into 
require_auth.  The fact that the methods in pg_hba.conf are not what 
libpq sees is not something that was really exposed to users until now. 
"none" vs. "trust" takes advantage of that.  But then I think we could 
also make "password" clearer, which surely sounds like any kind of 
password, encrypted or not, and that's also how pg_hba.conf behaves. 
The protocol specification calls that "AuthenticationCleartextPassword"; 
maybe we could pick a name based on that.

And then, what if we add a new method in the future, and someone puts 
that into their connection string.  Old clients will just refuse to 
parse that.  Ok, that effectively gives you the same behavior as 
rejecting the server's authentication offer.  But what about the negated 
version?  Also, what if we add new SASL methods.  How would we modify 
this code to be able to pick and choose and also have backward and 
forward compatible behavior?

In general, I like this.  We just need to think about the above things a 
bit more.