Different way of maintaining users?

We are considering a change to the way our users access the database and
our applications. We would like to make sure that users are getting to
the data through the applications only and not using external tools
(i.e. SQL*Plus) to access the database directly with the hopes that this
will help us to further secure our databases. In this scenario, we would
create a high-level user which would be the data source user (we're
using Cold Fusion for our application front-end) that would be able to
run any query on behalf of the user "logged in" to the application.
However, each user would not have his/her own DB account that requires
role and password maintenance. Instead, the programmers would create a
user and role table in the database that would hold this information
(including encrypted passwords) so that the users do not have individual
access to the database.  That would push a lot of the user maintenance
that I deal with on a daily basis to either our programmers or a help
desk technician. 
My question is whether or not this is a sound plan and if you have any
concerns about problems we might encounter if we decide to go this
route? Has anyone else done something similar in their environment?

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