You will find a variety of terraform configurations which you can use "as-is" or as a reference. There is a sample for just about every resource type in this repository.
I've taken the examples from this blog post: https://www.fastly.com/blog/10-pro-tips-for-getting-the-most-out-of-your-next-gen-waf And converted them into terraform files. These files alone will give you a great starting point in terms of WAF protection.
A link to the provider documentation can be found here: https://registry.terraform.io/providers/signalsciences/sigsci/latest/docs