title: How do I easily append text to an existing file on my server?
body: <p>I'd like to append some text from my iPhone app, to a file that already exists on my webserver.  What's the easiest way to do so?  I don't want you to write me code, just give me pointers on where to start and what I need running on my webserver (PHP?)</p>
  
  <p>Initially, each app can post to a different file (i can figure out some unique identifier to help me with this).  Later I may wish to have all the data written to the same file, in which case I would need to be careful of concurrent access.  </p>
  
  <p>Also, I am not sure how authentication should work; should I require each user or app to have a different account and password, which would be hard to do since then I would need a way to create accounts from within the app.  Or I could embed a default username&amp;password for all users, into the app - but that may open me up to some security issues.</p>
  
  <p>What else am I missing?</p>
  
  <p>EDIT:  I'm dropping the iOS tag as I think that this is more of a webserver question, and not an iOS question.</p>