This is an example repository using TFstate.dev.
In the terraform {} block of main.tf, there is an http backend which is configured as-per the instructions on our website.
Also, there is a terraform_remote_state data source, which uses the state output from example.
Access to the terraform_remote_state can be configured using the TF_HTTP_PASSWORD enviornment variable:
export TF_HTTP_PASSWORD="{your-github-token}"
terraform plan
terraform apply