auth-mysql and WordPress

I have what is likely a non-common situation. I’m setting up a WordPress site for someone but it’s for a limited audience and is even running on an SSL (i.e. https) site. The site uses basic authentication but the passwords are saved in a MySQL database. This is separate from the wordpress database although I suppose it could be added to that if it would be easier. I’m using Apache (2.0) and auth_mysql for that. It’s working as it should.

Now, the user would like the ability to modify the passwords from within wordpress. I have done a fair amount of PHP work so I can probably get this going but have never written a plugin for WP. So, I thought I’d check if this would be reinventing the wheel. Is there anything like this anywhere? If not, I’ll see what I can come up with. Are there plugin writing tutorials anywhere? How about a plugin that connects to a mysql database that I can use as a starting point?

Or should I just write a stand-alone PHP page and put it outside the wordpress tree?