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Legacy client authentication methods utilized.

Default Severity: high

Explanation

It is recommended to use Service Accounts and OAuth as authentication methods for accessing the master in the container cluster.

Basic authentication should be disabled by explicitly unsetting the username and password on the master_auth block.

Possible Impact

Username/password or certificate authentication methods are less secure

Suggested Resolution

Use service account or OAuth for authentication

Insecure Example

The following example will fail the google-gke-no-legacy-authentication check. 

 resource "google_service_account" "default" {
   account_id   = "service-account-id"
   display_name = "Service Account"
 }

 resource "google_container_cluster" "good_example" {
   name     = "my-gke-cluster"
   location = "us-central1"

   # We can't create a cluster with no node pool defined, but we want to only use
   # separately managed node pools. So we create the smallest possible default
   # node pool and immediately delete it.
   remove_default_node_pool = true
   initial_node_count       = 1
   master_auth {
     client_certificate_config {
       issue_client_certificate = true
     }
   }
 }

 resource "google_container_node_pool" "primary_preemptible_nodes" {
   name       = "my-node-pool"
   location   = "us-central1"
   cluster    = google_container_cluster.primary.name
   node_count = 1

   node_config {
     preemptible  = true
     machine_type = "e2-medium"

     # Google recommends custom service accounts that have cloud-platform scope and permissions granted via IAM Roles.
     service_account = google_service_account.default.email
     oauth_scopes    = [
       "https://www.googleapis.com/auth/cloud-platform"
     ]
   }
 }

Secure Example

The following example will pass the google-gke-no-legacy-authentication check. 

 resource "google_service_account" "default" {
   account_id   = "service-account-id"
   display_name = "Service Account"
 }

 resource "google_container_cluster" "good_example" {
   name     = "my-gke-cluster"
   location = "us-central1"

   # We can't create a cluster with no node pool defined, but we want to only use
   # separately managed node pools. So we create the smallest possible default
   # node pool and immediately delete it.
   remove_default_node_pool = true
   initial_node_count       = 1
 }

 resource "google_container_node_pool" "primary_preemptible_nodes" {
   name       = "my-node-pool"
   location   = "us-central1"
   cluster    = google_container_cluster.primary.name
   node_count = 1

   node_config {
     preemptible  = true
     machine_type = "e2-medium"

     # Google recommends custom service accounts that have cloud-platform scope and permissions granted via IAM Roles.
     service_account = google_service_account.default.email
     oauth_scopes    = [
       "https://www.googleapis.com/auth/cloud-platform"
     ]
   }
 }