title: Make parameter input required in CloudFormation template
body: <p>I have a template for AWS Cloud Formation. In this template I have set several parameters.
  Now, what I would like to do is to leave a parameter field empty but allow the user to select
  a specific parameter for example a security group. Now what I would like to do is that if 
  a user does not select anything (field stays empty) I want it to give an error message saying 
  field required when you want to proceed and prevent the user from proceeding, as it happens when you do not enter a stack name (see screenshot below).</p>
  
  <p><a href="https://i.stack.imgur.com/jPaTl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jPaTl.png" alt="enter image description here"></a></p>
  
  <p>How do I do this for any parameter in a cloud formation template??? I have searched around but do not find anything 
  regarding validation of user input … </p>
  
  <p>I know I could set a default for everything, but I do not want to set a default and specifically force
  a user to make a selection in this case …</p>