How to prevent terraform developers from viewing secrets with the nonsensitive function

It seems there's a lot of information out there on how to retrieve and view sensitive data in terraform, but not a lot on how to prevent viewing of it via the nonsensitive function.

For example, suppose I have a secret stored in Azure Key Vault and I want my config to grab it and use it somewhere:

data "azurerm_key_vault_secret" "my_ultra_secret" {
    name         = "my_ultra_secret"
    key_vault_id = data.azurerm_key_vault.mykeyvault.id
}

(I'm using remote state stored in HCP Terraform, aka Terraform Cloud, with a service principal for Terraform to talk to Azure and manipulate resources.)

If a developer is able to get this code and go into terraform console, they can do this:

nonsensitive(data.azurerm_key_vault_secret.my_ultra_secret)

Thus exposing the secret in plain text. I don't want the developer seeing the secrets, but obviously terraform cloud needs to, so the idea of restricting my service principal's permissions doesn't seem to fit the bill.

Any idea how I do this? (I've looked at dynamic provider credentialing, but this doesn't seem to restrict permissions based on user, as far as I can tell.

After experimenting with various options, I think I have a fairly good solution. The documentation for HCP Cloud on these options is here, but I will translate into my own words in case that helps anyone.

TL;DR: HCP cloud provides granular RBAC to control the things I talked about in the OP.

• Keep in mind with HCP Cloud, there are two sets of credentials to manage: your HCP/terraform creds, and your Azure/whatever provider creds. These both can come into play while working in terraform, but for the purposes of this answer, we're concerned only about the former. HCP cloud determines who a user is when they run terraform login, and that's what you'll use to set these RBAC settings. The latter is controlled with az login, but again, out of scope for this answer.
• If you have a service provider set up linking Azure and HCP Cloud (I hope you do), then that will continue to work as per the RBAC settings in Azure that you've set up. All the bullets below are purely concerned about developer access to your terraform workspaces, not to Azure.
• If you want to block access to the terraform console completely and keep that Pandora's box closed, make sure to uncheck this option when setting up a team's permissions. This will effectively block any developer from being able to enter the console and view data that way. Note they may still be able to see some secrets using terraform output (more on that below).
• If you want to allow access to the console, you can also separately block access to state. Here is the solution to my original quandary: if you set "no access" or "read outputs only," then any sensitive values that you try to expose via the nonsensitive function will simply show (known after apply). If you allow full read access, then they will be able to see your secrets.
  
• Do note though, that if you have sensitive values in output variables, setting "read outputs only" will let them view those secrets with a command like terraform output myvar. If you set state to "no access," then the previous command will show No outputs found.
• There are also options to control access to input variables, but that's beyond the scope of this question.

This answer doesn't address any general security best practices when it comes to Terraform secrets, as you can find those all over the place.

Hope this helps!