I want to display a message in a block for unauthenticated users and a different message for authenticated users. 

Does anyone know of a module or method to solve this fairly common use case with ony ONE block. 

I think the obvious solution for this is to create two blocks with two different visibility rules. I've had to do this in a number of cases. But, it seems a bit hacky. In Backdrop layouts can quickly get cluttered with conditional blocks and I think the opportunity to reduce the number of blocks needed would be worth it. 

This seems like a common enough use case and potentially not that had to create.

Does such a module exist for Backdrop or Drupal?

I did find this interesting idea, which might be better, because this could work in a block or a regular node page. 
https://www.drupal.org/project/conditional_text

Comments

So I took the basic idea for this module and created a brand new contrib module. https://github.com/backdrop-contrib/conditional_content_block

This module works, but I'm not that at experienced at creating modules from scratch so I would love help and feedback pointing out:

1) What kinds of things does a contrib module need to think about that a simple custom module for private use doesn't.

2) Feature ideas. 

Right now, it's very simple. The module provides a block with two text fields. One text field displays to authenticated users and one to unauthenticated users. 

I would like to provide additional "conditions" as well. Also, I would like to allow the block to use existing content. 

What else should a block like this do?

Current Title: Conditional Content Block

I'm not excited about the name of the module. Suggestions?