integrating login for wordpress and a custom php app on same server.

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PHP

MySQL

WordPress

Hi all,
I have a question around user login & registration strategies.

I have a site in the making that has a wordpress blog. Along with this blog I have several custom Web Apps that I want to add to the same site.

The folder structure on the site looks like:

www.mysite.com/wp
www.mysite.com/myfirstapp
www.mysite.com/mysecondapp

There are two MySQL databases: the wordpress db 'wordpress' and another for the two apps 'appdb' The non wordpress apps run the same custom framework for extensibility etc.

I want a single registration & authentication using the following functionality:

I want to leverage the wordpress's login and registration system so that On registering a user from wordpress, a script runs to update a user table in 'appdb' with the newly registered user... the wordpress software takes care of all of the authentication and registration functionality.

I can foresee headaches dealing with cookies and session variables etc though.

My question is this:
Has anyone done this already and any help you can give is appreciated

Just to clarify that I already have a custom authentication and registration functionality within the non wordpress apps. When I wrote the framework code I did it for completeness. One solution I am looking into is not touching wordpress and creating a new class to interface with wpress to carry out all functions

all help etc. appreciated