It's taken longer than I would have liked, but my book "OAuth 2.0 Simplified" is finally available! https://oauth2simplified.com
We did a pre-launch at Okta's conference in Las Vegas in August, and it's taken a bit longer to sort out the details of actually listing it for sale. It's available for purchase right now at the website, and will be visible on Amazon.com in 6-8 weeks.
Next I'm working out the logistics of publishing an ePub/Kindle version, which it turns out is not just pushing the "ebook" button. This has been a fascinating process to learn about!