title: Facebook IFrame App Validating Registration Form Fields
body: <p>I'm creating a website in C# ASP.NET and I'm trying to integrate Facebook. I've used a Facebook IFrame as my registration form and the Facebook C# SDK here <a href="http://facebooksdk.codeplex.com/" rel="nofollow">http://facebooksdk.codeplex.com/</a> to access Facebook user details. So far I've figured out how to add the fields I require in the Facebook IFrame, and using the SDK I know how to decrypt the data posted back to me from the signed request field server side.</p>
  
  <p>My question is how can I add validation to the fields before they are posted? It seems that the password field I've added to the Facebook IFrame registration form already has some validation since the password must be at least 8 characters, but I'm not sure how this is being done or if/how I can possibly customise it.</p>
  
  <p>Hopefully someone out there can help point me in the right direction. Thanks for reading.</p>