Terraform
These projects from the OPA ecosystem integrate OPA with either Terraform source code in HCL or Terraform plans in JSON.
Styra Declarative Authorization Service
Styra DAS has native support for the validation of Terraform code and plans via a prebuilt 'system-type', this is documented here.
Conftest
Conftest has generic support for Terraform source files defined in HCL. There is an example provided here on GitHub.
env0
env0 is a Terraform automation platform that allows you to manage your infrastructure as code (IaC) at scale. It has a built-in integration with OPA. See docs here.
Scalr
These policies can be run using OPA at the command line against a Terraform plan JSON. See the example in the README.
Spacelift
Spacelift supports Rego as a language to describe policies for Terraform JSON plans. This blog outlines how the integration works.
Torque
Torque supports Terraform policy enforcement and defines some sample policies here.
Atmos
Atmos can validate Terraform stack before applying them. This is done
using the validate component command
documented here.
Terraform Cloud
Terraform cloud has native support for enforcing Rego policy on plans. The feature is documented here.