What are you trying to do more exactly, shinypixel? ("...that I can read/write to it")
Reading sounds like requesting a file with the normal methods (HTTP/S).
"...that can be a security issue..." but it's usually not. You have to take care that your webserver software is uptodate and your configuration doesn't leave any vulnerabilities. That's very achievable and much can be learned by reading docs and forums.
"Write" on the other hand is a bit more tricky. I agree with nfactorial and spazzarama, that suggets a proper API (REST*, RPC) with access control. On the other hand, that is not as difficult as it may seem, because it has been done many times before. You'll find lots of information on the net and you can learn a great deal.
If you are not set on Microsoft technologies for your backend, I'd suggest Apache/MySQL/PHP (WAMP, MAMP, LAMP). It's easy to set up, get into and have quick results when prototyping.