For those who might want to try this: a couple points about how glitch.com works regarding the public vs private visibility of the JSON data files in the glitch app. I added these comments to the app’s README.md.
Note that unless you make your project private, your JSON files will be copied over to anyone who remixes your project. See this glitch help topic for more info and instructions on how to make your project private if you wish to do so. Your blog is probably public anyway, but you have the choice whether to keep these JSON files private or not.
If you want to keep your project public, but don’t want your JSON data files to be available to others who remix your project, you can put the data files in a special .data folder, which is not copied over or visible to others when a project is remixed.
If you put your JSON files in .data, you must reference them accordingly in the index.php program. Here is an example:
$blog[0] = array("fn" => ".data/wa-posts.json", "href" => "https://write.as/", "md_ext" => '.md');
As an example, this project has the JSON data file stored in the .data folder. If you remix this app, you’ll need to create the .data folder and add the JSON file(s) to it per the glitch help message referenced above.