Kent, I got this working. I have suggestions for the template your post:
1. the title is slightly misleading, the flow is actually getting messages about incidents shown on the Service Health page, I was expecting to get Messages from the Message Center pages. It would be helpful to clarify this in the template.
I'm going to play around with making some changes to get the Messages also.
2. I was getting errors from the Client Secret variable. It turned out that I needed to use the encodeUriComponent function because my secret had special characters (a + and an = ). I'm sure that this will trip other people up so calling it out in the blog post would be helpful, or baking it into the template would be even better.
Dean