Use a CloudFront keypair instead of root keys

.gitignore

@@ -7,3 +7,4 @@ infra/terraform.tfstate*
 infra/terraform.tfvars
 infra/backend.tf
 infra/templates/email-invite.html
+infra/*.pem

README.md

@@ -66,48 +66,27 @@ cd lambda
 ./build.sh
 ```
 
-### 4. Setup your CloudFront private key
+### 4. Create a CloudFront key pair
 
 Authentication relies on cookies signed with a key pair.
-This is a sensitive value, so the stack expects it to be stored encrypted in
-[SSM Parameter Store](https://docs.aws.amazon.com/systems-manager/latest/userguide/systems-manager-paramstore.html).
-
-First, generate a new key pair locally:
+You must generate a new one locally:
 
 ``` bash
+cd infra
 openssl genrsa -out private_key.pem 2048
 openssl rsa -pubout -in private_key.pem -out public_key.pem
 ```
 
-Then store the public key on CloudFront:
-
-1. Open the CloudFront UI
-2. Navigate to "Key management", then "Public keys"
-3. Upload the public key, and take note of the Key ID you receive
-4. Navigate to the "Key group" section just underneath
-5. Create a new key group which includes the public key above
-
-Then store the values in Parameter Store:
-
-1. Open the Parameter Store UI
-2. Create the 2 following entries:
+These keys will be deployed as part of the infrastructure. AWS recommends rotating them every 3 months.
 
-| Name | Type | KMS Key ID | Value | Example |
-|------|------|------------|-------|---------|
-| `cloudfront_keypair_id`  | `String` | - | Public ID of the key pair | `ABC123456789` |
-| `cloudfront_private_key` | `Secure String` | `alias/aws/ssm` | Contents of the private key | `-----BEGIN RSA PRIVATE KEY-----`<br />`...`<br/>`-----END RSA PRIVATE KEY-----` |
-
-You should then delete the private key you have downloaded.
-AWS recommends rotating this key pair every 3 months.
-
-*Note:* the Parameter Store values are cached in the Lambda function to speed up invocation.
+Note: the values are cached by the Lambda function (in memory) to speed up invocation.
 When you rotate the key pair, the old value will still be used until the next **Lambda cold start**.
 You can re-deploy the Lambda function to force a cold-start.
 
-### 4. Deploy infrastructure
+### 5. Deploy infrastructure
 
 The whole infrastructure is written as [Terraform](https://www.terraform.io/) templates.
-First, authenticate against AWS with the [AWS CLI](https://aws.amazon.com/cli‎):
+First, authenticate against AWS with the [AWS CLI](https://aws.amazon.com/cli):
 
 - run `aws configure` and enter the access key and secret key
 - if you saved your credentials as a non-default profile, run `export AWS_PROFILE=profile_name`
@@ -121,13 +100,7 @@ terraform apply
 ```
 
 If you make any subsequent changes, simply re-run `terraform apply` to apply the update.
-
-!!NOTE!! The code has not yet been updated to take advantage of CloudFront Keypairs.
-Once deployed, you must:
-
-- go into the CloudFront distribution
-- edit the "behaviours" section for **HTML** and **Default**
-- update `Trusted authorization type` from `Self` to the keygroup you created above
+The Terraform code relies on `public_key.pem` and `private_key.pem` existing in the `infra` folder.
 
 ### 6. Create users
 

infra/cloudfront.tf

@@ -5,6 +5,18 @@ data "aws_acm_certificate" "domain" {
   most_recent = true
 }
 
+resource "aws_cloudfront_public_key" "cookie_signer" {
+  comment     = "Cookie signer public key"
+  encoded_key = file("public_key.pem")
+  name        = "cookie-signer"
+}
+
+resource "aws_cloudfront_key_group" "cookie_signer" {
+  comment = "example key group"
+  items   = [aws_cloudfront_public_key.cookie_signer.id]
+  name    = "cookie-signer"
+}
+
 resource "aws_cloudfront_distribution" "distribution" {
   aliases             = ["${var.website_domain}"]
   price_class         = "PriceClass_100"
@@ -87,7 +99,7 @@ resource "aws_cloudfront_distribution" "distribution" {
     path_pattern                = "/api/*"
     smooth_streaming            = false
     target_origin_id            = "Login API gateway"
-    trusted_signers             = []
+    trusted_key_groups          = [aws_cloudfront_key_group.cookie_signer.name]
     viewer_protocol_policy      = "https-only"
 
     forwarded_values {
@@ -142,7 +154,7 @@ resource "aws_cloudfront_distribution" "distribution" {
     min_ttl                     = 15552000
     smooth_streaming            = false
     target_origin_id            = "S3-${var.s3_bucket_name}"
-    trusted_signers             = ["self"]
+    trusted_key_groups          = [aws_cloudfront_key_group.cookie_signer.name]
     lambda_function_association = []
     viewer_protocol_policy      = "redirect-to-https"
 

infra/parameterstore.tf

@@ -0,0 +1,13 @@
+resource "aws_ssm_parameter" "keypair_id" {
+  name        = "cloudfront_keypair_id"
+  description = "ID of the public key in CloudFront"
+  type        = "String"
+  value.      = aws_cloudfront_public_key.cookie_signer.id
+}
+
+resource "aws_ssm_parameter" "private_key" {
+  name        = "cloudfront_private_key"
+  description = "Private key for signing CloudFront cookies"
+  type        = "SecureString"
+  value       = file("private_key.pem")
+}