What's the proper Tornado response for a log in success?
You can send your response with either self.write() or self.finish() (the main difference is that with write() you can assemble your response in several pieces, while finish() can only be called once.  You also have to call finish() once if you're using asynchronous functions that are not coroutines, but in most cases it is done automatically).  
As for what to send, it doesn't really matter if it's a non-browser application that only looks at the status code, but I generally send an empty json dictionary for cases like this so there is well-defined space for future expansion.
So far I have a pretty basic server (I haven't built in any security features yet, like cookie authentication). What I've got so far is an iOS app where you enter a username and password and those arguments are plugged into a URL and passed to a server. The server checks to see if the username is in the database and then sends a confirmation to the app. Pretty basic but what I can't figure out is what the confirmation should look like?
The server is a Python Tornado server with a MySQL dbms.. 
What I'm unsure of is what Tornado should/can send in response? Do I use self.write or self.response or self.render? I don't think it's self.render because I'm not rendering an HTML file, I'm just sending the native iOS app a confirmation response which, once received by the app, will prompt it to load the next View Controller.
After a lot of googling I can't seem to find the answer (probably because I don't know how to word the question correctly). 
I'm new to servers so I appreciate your patience.