PrivateKey Format in Terraform Cloud

I am using the OCI provider and Terraform Cloud. OCI requires a private_key_path or private_key.
I would like to store the key as a sensitive variable in Terraform Cloud Environment Variables or regular Variables. However, I keep getting invalid format as an error. I remove all new lines and I still get it.
It does work if I assign a path to the folder with it but then I am storing the key in GitHub.
What format of pem key does Terraform Cloud take as just plain text (and then mark sensitive) or if there is a better way to store the key?