Actually that's exactly what we do with LedgerSMB. The database is the final enforcer of security matters and the authoritative voice in authentication (the web app logs into the db with user-supplied credentials). A lot of traditional middleware functions are pushed into the db (as stored procedures) where these can be reasonably represented as set operations against the database. As an ERP application, this means that this includes just about everything except generating printable invoices or HTML.
This works well. There are some things we are still working on improving, but it's getting there. Moreover it means multiple clients on multiple codebases are possible and we don't have to worry as much about the implications of what happens when someone writes a secondary client to hit the database.
At the same time, we use PostgreSQL, which I have a bit more confidence in than MySQL. Of course I would still suggest limiting access only to those IP address ranges where that is necessary.
Oh god you poor man. We took a look at using SMB Ledger (the parent of LedgerSMB) years back and after peeling back the covers it just looked horrific both from a security and general code quality perspective. This was around the time of the fork, and I couldn't help feel that SMB Ledger had it's work cut out. Hopefully you guys have been able to get through to the other side.
1) Going to a db-centric security model has allowed us not to trust the SQL-Ledger code (good thing too).
2) We are refactoring/removing SQL-Ledger code as quickly as possible. As of 1.3 this means payment logic, reconciliation logic, contact management logic and more. 1.4 will hopefully rip out and replace all search and reporting functions. It will take us a few more years to get the codebase where we want it though.
3) The bad thing about bad code is that bad code is contagious. When you spend a lot of your time debugging bad code it is very hard to write good code. Most of what we wrote for 1.3 will need to be rewritten again. I am pretty happy with the code we are writing for 1.4.....
I think we have come through the worst of it. Pace of development is speeding up which is a good sign and much more of the application is subjected to unit tests.
As a side note, when we first added unit tests to the number rounding tests for the code we inherited from SQL-Ledger, there were failures. We replaced that logic very quickly.
Yeah, it was pretty bad... Now its getting better.
Edit: Also it seems to me the worst never seems so bad when you are in it. I don't think that I could see how many problems we had from this until I am here, half way from 1.3 to 1.4, asking why 1.3 took five years to release (we beat Perl 6 and HURD though, I guess Duke Nukem Forever in fact beat us date-wise by a couple months).
Looking back at the customers of mine who have had problems, or projects that went way over budget or took too long because of difficulties here, I can see how much that hurt us. At the time though, it was just one of those keep working on it kind of things.
This works well. There are some things we are still working on improving, but it's getting there. Moreover it means multiple clients on multiple codebases are possible and we don't have to worry as much about the implications of what happens when someone writes a secondary client to hit the database.
At the same time, we use PostgreSQL, which I have a bit more confidence in than MySQL. Of course I would still suggest limiting access only to those IP address ranges where that is necessary.