Automating access grants

I need advice, and a lot of it, from those with more experience, since
I have practically none. Please, let me know your opinion on the
following.

We have an in-house Postgres database that we would like to make
publicly accessible via a password-less login (user: anonymous). (We
already have a web front-end for this database, but we have had a lot
of requests to allow programmatic access in a way that does not
require scraping web pages; FWIW, web scraping of this site is already
disallowed in our TOS.)

The problem is how to make this database publicly accessible in a way
that protects our server from abuse, and at the same time minimizes
the amount of time we have to spend policing it.

One possible solution (that I like) would be to require some sort of
host registration[1] from potential users, so that password-less
connection attempts from only these hosts would be allowed. The
principal objective here would be to simplify the process of
identifying and neutralizing any abuse to the system.

My thought would be to set up a registration webpage page with
safeguards to prevent robots from registering, maybe perform other
checks (such as ensuring that the email address given is legit), and
spool the registration requests for processing. (BTW, does anyone
know of free software to do this?)

Now, supposing we have a fresh batch of host registration requests
that have passed all the filters we may impose on them (i.e. they have
been "approved" somehow). How best to automate the process of
granting access to these host? I suppose that the script/program in
charge of this could, in principle, update the pg_hba.conf file, and
bounce the server with a suitable "kill -HUP", but I'm queasy about
such unsupervised bouncing of the server. I could use some words of
wisdom on this topic.

More generally, are we even on the right track here? Or is the whole
idea of making our database publicly accessible totally foolish?

Are there any examples that I may be able to learn from?

We are specifically trying to avoid, at this initial stage at least,
any solution that would require creating a proxy server for the sole
purpose of authenticating and/or validating requests (e.g. ensuring
that the request include a unique key, etc.) Our hope is that we may
be able to craft a solution using only PostgreSQL's standard security
facilities that would be adequate for at least the first several
months of operation, if not much longer.

Many thanks for your thoughts and opinions on this!

kj

[1] I realize that it may inconvenient for the anonymous users to be
restricted to one or a few hosts, but the kinds of uses of our
database that we consider legitimate should be possible even with this
inconvenience.