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Managing Secrets in Infrastructure As Code with Terraform

ยท 4 min read
AppSec Engineer

Okay, you've moved your infrastructure provisioning from visiting the console page and now adopted IaC ( Infrastructure as Code) for provisioning your infrastructure using Terraform.

So along the way, you discovered that you will need some sensitive credentials like GitHub token to use with aws amplify, datadog API and key deployments?

well, there are various approaches to getting the secrets to our IaC, and the first approach I believe you would want to use is putting the API keys in your codes as variables which is a bad approach.

the next approach I believe you want to use is setting an empty variable and passing the values via CLI just like this.
variable "githubtoken" {
description = "github token"
type = string

And then pass the value using export TF_VAR_githubtoken=xxxxxxxx

As time goes on, you will notice this process isn't so healthy because you are burdened to always keep the secret somewhere on your work laptop and also the need to always reexport those variables, having them in your shell history too.

But you can always solve this issue using AWS SSM Parameter Store, and it makes more sense if your Infrastructure is on AWS already.

So let's jump into it;

๐Ÿ‘‰ Create Secrets in the Parameter Storeโ€‹

First, you would need to create the secret value on the Secret Parameter Store via your aws console or aws cli

aws ssm put-parameter --name /staging/terraform/githubtoken --value ghp_xxxxxxx --type SecureString --region AWS_REGION_VALUE

The above command would create your secrets in the parameter store, likewise, you can create it via the was console too.

parameter store aws console

Once you are done with adding your secrets, you need to get it back to use where you need it, which is in our terraform code.

๐Ÿ‘‰ Use secrets in Terraformโ€‹

Now, you have to retrieve the secret you created earlier in the parameter store using the following terraform code.
data "aws_ssm_parameter" "github_token" {
name = "/staging/terraform/githubtoken"

You will now have to pass the value from the secret data source for parameter store recreation, instead of passing the value straight to the service needing the secret.

The reason for this is to try and separate how the service accesses the secrets, so a recreation of that parameter store value will serve as a procedural process, so if the secrets are not available, an error will be thrown.
resource "aws_ssm_parameter" "staging_github_token" {
name = "/staging/terraform/github_token"
value = data.aws_ssm_parameter.github_token.value // depending on value of data source from above code
type = "SecureString"

Now let's put the secret we've recreated to use by calling it via data source and passing it into the resource that needs it.
data "aws_ssm_parameter" "staging_github_token" {
name = "/staging/terraform/github_token"

resource "resource_that_need_secret" "secret_needed_here" {
access_token = data.aws_ssm_parameter.staging_github_token.value

๐Ÿ‘‰ Using the secrets with terraform providerโ€‹

Bet you want to pass the secret to the provider too just like you did with resources, but definately it won't work, because dependencies in Terraform don't work with providers in Terraform yet.
data "aws_ssm_parameter" "staging_github_token" {
name = "/staging/terraform/github_token"

provider "github" {
token = data.aws_ssm_parameter.staging_github_token.value

So how would you go about it? you will have to create a separate terraform deployment and make the value from the parameter store data source as an output value alongside using the sensitive value as true, because that's a secret we don't want to make public.
data "aws_ssm_parameter" "staging_github_token" {
name = "/staging/terraform/github_token"

output "staging_github_token" {
value = data.aws_ssm_parameter.staging_github_token.value
sensitive = true

Now it's time to pass the value to the provider that needs it, which is your deployment that has a provider that needs GitHub token value.
data "terraform_remote_state" "another_deployment" {
// put your terraform state backend config here

provider "github" {
token = data.terraform_remote_state.another_deployment.staging_github_token.value

That's all for now, I hope you've learned something useful from this blog about secret management in IaC with Terraform.

Till next time โœŒ๏ธ