Implement Service Account Impersonation

third_party/terraform/utils/config.go.erb

@@ -58,6 +58,7 @@ import (
 	sqladmin "google.golang.org/api/sqladmin/v1beta4"
 	"google.golang.org/api/storage/v1"
 	"google.golang.org/api/storagetransfer/v1"
+	"google.golang.org/api/transport"
 )
 
 type providerMeta struct {
@@ -67,16 +68,18 @@ type providerMeta struct {
 // Config is the configuration structure used to instantiate the Google
 // provider.
 type Config struct {
-	Credentials 	 	string
-	AccessToken 	 	string
-	Project     	 	string
-	BillingProject      string
-	Region      	 	string
-	Zone        	 	string
-	Scopes         		[]string
-	BatchingConfig		*batchingConfig
-	UserProjectOverride bool
-	RequestTimeout  time.Duration
+	AccessToken                         string
+	Credentials                         string
+	ImpersonateServiceAccount           string
+	ImpersonateServiceAccountDelegates  []string
+	Project                             string
+	Region                              string
+	BillingProject                      string
+	Zone                                string
+	Scopes                              []string
+	BatchingConfig                      *batchingConfig
+	UserProjectOverride                 bool
+	RequestTimeout                      time.Duration
 	// PollInterval is passed to resource.StateChangeConf in common_operation.go
 	// It controls the interval at which we poll for successful operations
 	PollInterval time.Duration
@@ -711,19 +714,29 @@ func (c *Config) NewServiceUsageClient(userAgent string) *serviceusage.Service {
 
 // staticTokenSource is used to be able to identify static token sources without reflection.
 type staticTokenSource struct {
-	oauth2.TokenSource
+      oauth2.TokenSource
 }
 
 func (c *Config) GetCredentials(clientScopes []string) (googleoauth.Credentials, error) {
+
 	if c.AccessToken != "" {
 		contents, _, err := pathOrContents(c.AccessToken)
 		if err != nil {
 			return googleoauth.Credentials{}, fmt.Errorf("Error loading access token: %s", err)
 		}
+		token := &oauth2.Token{AccessToken: contents}
+
+		if c.ImpersonateServiceAccount != "" {
+			opts := []option.ClientOption{option.WithTokenSource(oauth2.StaticTokenSource(token)), option.ImpersonateCredentials(c.ImpersonateServiceAccount, c.ImpersonateServiceAccountDelegates...), option.WithScopes(clientScopes...)}
+			creds, err := transport.Creds(context.TODO(), opts...)
+			if err != nil {
+				return googleoauth.Credentials{}, err
+			}
+			return *creds, nil
+		}
 
 		log.Printf("[INFO] Authenticating using configured Google JSON 'access_token'...")
 		log.Printf("[INFO]   -- Scopes: %s", clientScopes)
-		token := &oauth2.Token{AccessToken: contents}
 
 		return googleoauth.Credentials{
 			TokenSource: staticTokenSource{oauth2.StaticTokenSource(token)},
@@ -735,7 +748,14 @@ func (c *Config) GetCredentials(clientScopes []string) (googleoauth.Credentials,
 		if err != nil {
 			return googleoauth.Credentials{}, fmt.Errorf("error loading credentials: %s", err)
 		}
-
+		if c.ImpersonateServiceAccount != "" {
+			opts := []option.ClientOption{option.WithCredentialsJSON([]byte(contents)), option.ImpersonateCredentials(c.ImpersonateServiceAccount, c.ImpersonateServiceAccountDelegates...), option.WithScopes(clientScopes...)}
+			creds, err := transport.Creds(context.TODO(), opts...)
+			if err != nil {
+				return googleoauth.Credentials{}, err
+			}
+			return *creds, nil
+		}
 		creds, err := googleoauth.CredentialsFromJSON(c.context, []byte(contents), clientScopes...)
 		if err != nil {
 			return googleoauth.Credentials{}, fmt.Errorf("unable to parse credentials from '%s': %s", contents, err)
@@ -746,6 +766,16 @@ func (c *Config) GetCredentials(clientScopes []string) (googleoauth.Credentials,
 		return *creds, nil
 	}
 
+	if c.ImpersonateServiceAccount != "" {
+		opts := option.ImpersonateCredentials(c.ImpersonateServiceAccount, c.ImpersonateServiceAccountDelegates...)
+		creds, err := transport.Creds(context.TODO(), opts, option.WithScopes(clientScopes...))
+		if err != nil {
+			return googleoauth.Credentials{}, err
+		}
+		return *creds, nil
+
+	}
+
 	log.Printf("[INFO] Authenticating using DefaultClient...")
 	log.Printf("[INFO]   -- Scopes: %s", clientScopes)
 

third_party/terraform/utils/config_test.go

@@ -90,6 +90,76 @@ func TestAccConfigLoadValidate_credentials(t *testing.T) {
 	}
 }
 
+func TestAccConfigLoadValidate_impersonated(t *testing.T) {
+	if os.Getenv(TestEnvVar) == "" {
+		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
+	}
+	testAccPreCheck(t)
+
+	serviceaccount := multiEnvSearch([]string{"IMPERSONATE_SERVICE_ACCOUNT_ACCTEST"})
+	creds := getTestCredsFromEnv()
+	proj := getTestProjectFromEnv()
+
+	config := &Config{
+		Credentials:               creds,
+		ImpersonateServiceAccount: serviceaccount,
+		Project:                   proj,
+		Region:                    "us-central1",
+	}
+
+	ConfigureBasePaths(config)
+
+	err := config.LoadAndValidate(context.Background())
+	if err != nil {
+		t.Fatalf("error: %v", err)
+	}
+
+	_, err = config.NewComputeClient(config.userAgent).Zones.Get(proj, "us-central1-a").Do()
+	if err != nil {
+		t.Fatalf("expected API call with loaded config to work, got error: %s", err)
+	}
+}
+
+func TestAccConfigLoadValidate_accessTokenImpersonated(t *testing.T) {
+	if os.Getenv(TestEnvVar) == "" {
+		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
+	}
+	testAccPreCheck(t)
+
+	creds := getTestCredsFromEnv()
+	proj := getTestProjectFromEnv()
+	serviceaccount := multiEnvSearch([]string{"IMPERSONATE_SERVICE_ACCOUNT_ACCTEST"})
+
+	c, err := google.CredentialsFromJSON(context.Background(), []byte(creds), DefaultClientScopes..)
+	if err != nil {
+		t.Fatalf("invalid test credentials: %s", err)
+	}
+
+	token, err := c.TokenSource.Token()
+	if err != nil {
+		t.Fatalf("Unable to generate test access token: %s", err)
+	}
+
+	config := &Config{
+		AccessToken:               token.AccessToken,
+		ImpersonateServiceAccount: serviceaccount,
+		Project:                   proj,
+		Region:                    "us-central1",
+	}
+
+	ConfigureBasePaths(config)
+
+	err = config.LoadAndValidate(context.Background())
+	if err != nil {
+		t.Fatalf("error: %v", err)
+	}
+
+	_, err = config.NewComputeClient(config.userAgent).Zones.Get(proj, "us-central1-a").Do()
+	if err != nil {
+		t.Fatalf("expected API call with loaded config to work, got error: %s", err)
+	}
+}
+
 func TestAccConfigLoadValidate_accessToken(t *testing.T) {
 	if os.Getenv(TestEnvVar) == "" {
 		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))

third_party/terraform/utils/provider.go.erb

@@ -41,6 +41,19 @@ func Provider() *schema.Provider {
 				}, nil),
 				ConflictsWith: []string{"credentials"},
 			},
+			"impersonate_service_account": {
+				Type:     schema.TypeString,
+				Optional: true,
+				DefaultFunc: schema.MultiEnvDefaultFunc([]string{
+					"GOOGLE_IMPERSONATE_SERVICE_ACCOUNT",
+				}, nil),
+			},
+
+			"impersonate_service_account_delegates": {
+				Type:     schema.TypeList,
+				Optional: true,
+				Elem:     &schema.Schema{Type: schema.TypeString},
+			},
 
 			"project": &schema.Schema{
 				Type:     schema.TypeString,
@@ -468,6 +481,9 @@ func providerConfigure(ctx context.Context, d *schema.ResourceData, p *schema.Pr
 		config.AccessToken = v.(string)
 	} else if v, ok := d.GetOk("credentials"); ok {
 		config.Credentials = v.(string)
+    }
+	if v, ok := d.GetOk("impersonate_service_account"); ok {
+		config.ImpersonateServiceAccount = v.(string)
 	}
 
 	scopes := d.Get("scopes").([]interface{})
@@ -478,6 +494,14 @@ func providerConfigure(ctx context.Context, d *schema.ResourceData, p *schema.Pr
 		config.Scopes[i] = scope.(string)
 	}
 
+	delegates := d.Get("impersonate_service_account_delegates").([]interface{})
+	if len(delegates) > 0 {
+		config.ImpersonateServiceAccountDelegates = make([]string, len(delegates))
+	}
+	for i, delegate := range delegates {
+		config.ImpersonateServiceAccountDelegates[i] = delegate.(string)
+	}
+
 	batchCfg, err := expandProviderBatchingConfig(d.Get("batching"))
 	if err != nil {
 		return nil, diag.FromErr(err)

third_party/terraform/website/docs/guides/provider_reference.html.markdown

@@ -18,7 +18,6 @@ location (`zone` and/or `region`) for your resources.
 
 ```hcl
 provider "google" {
-  credentials = file("account.json")
   project     = "my-project-id"
   region      = "us-central1"
   zone        = "us-central1-c"
@@ -27,7 +26,6 @@ provider "google" {
 
 ```hcl
 provider "google-beta" {
-  credentials = file("account.json")
   project     = "my-project-id"
   region      = "us-central1"
   zone        = "us-central1-c"
@@ -62,6 +60,29 @@ resource "google_compute_instance" "beta-instance" {
 provider "google-beta" {}
 ```
 
+## Authentication
+
+### Running Terraform on your workstation.
+
+If you are using terraform on your workstation, you will need to install the Google Cloud SDK and authenticate using [User Application Default
+Credentials](https://cloud.google.com/sdk/gcloud/reference/auth/application-default).
+
+A quota project must be set which gcloud automatically reads from the `core/project` value. You can override this project by specifying `--project` flag when running `gcloud auth application-default login`. The SDK should return this message if you have set the correct billing project. `Quota project "your-project" was added to ADC which can be used by Google client libraries for billing and quota.`
+
+### Running Terraform on Google Cloud
+
+If you are running terraform on Google Cloud, you can configure that instance or cluster to use a [Google Service
+Account](https://cloud.google.com/compute/docs/authentication). This will allow Terraform to authenticate to Google Cloud without having to bake in a separate
+credential/authentication file. Make sure that the scope of the VM/Cluster is set to cloud-platform.
+
+### Running Terraform outside of Google Cloud
+
+If you are running terraform outside of Google Cloud, generate a service account key and set the `GOOGLE_APPPLICATION_CREDENTIALS` environment variable to
+the path of the service account key. Terraform will use that key for authentication.
+
+### Impersonating Service Accounts
+
+Terraform can impersonate a Google Service Account as described [here](https://cloud.google.com/iam/docs/creating-short-lived-service-account-credentials). A valid credential must be provided as mentioned in the earlier section and that identity must have the `roles/iam.serviceAccountTokenCreator` role on the service account you are impersonating.
 
 ## Configuration Reference
 
@@ -72,15 +93,6 @@ same configuration.
 
 ### Quick Reference
 
-* `credentials` - (Optional) Either the path to or the contents of a
-[service account key file] in JSON format. You can
-[manage key files using the Cloud Console].  If not provided, the
-application default credentials will be used.  You can configure
-Application Default Credentials on your personal machine by
-running `gcloud auth application-default login`. If
-terraform is running on a GCP machine, and this value is unset,
-it will automatically use that machine's configured service account.
-
 * `project` - (Optional) The default project to manage resources in. If another
 project is specified on a resource, it will take precedence.
 
@@ -91,6 +103,13 @@ region is specified on a regional resource, it will take precedence.
 zone should be within the default region you specified. If another zone is
 specified on a zonal resource, it will take precedence.
 
+* `impersonate_service_account` - (Optional) The service account to impersonate for all Google API Calls.
+You must have `roles/iam.serviceAccountTokenCreator` role on that account for the impersonation to succeed.
+
+* `credentials` - (Optional) Either the path to or the contents of a
+[service account key file] in JSON format. You can
+[manage key files using the Cloud Console].  If not provided, the
+application default credentials will be used. 
 ---
 
 * `scopes` - (Optional) The list of OAuth 2.0 [scopes] requested when generating
@@ -166,9 +185,16 @@ are automatically available. See
 for more details.
 
 * On your computer, you can make your Google identity available by
-running [`gcloud auth application-default login`][gcloud adc]. This
-approach isn't recommended- some APIs are not compatible with
-credentials obtained through `gcloud`.
+running [`gcloud auth application-default login`][gcloud adc]. 
+
+---
+* `impersonate_service_account` - (Optional) The service account to impersonate for all Google API Calls.
+You must have `roles/iam.serviceAccountTokenCreator` role on that account for the impersonation to succeed. 
+If you are using a delegation chain, you can specify that using the `impersonate_service_account_delegates` field.
+Alternatively, this can be specified using the `GOOGLE_IMPERSONATE_SERVICE_ACCOUNT` environment
+variable.
+
+* `impersonate_service_account_delegates` - (Optional) The delegation chain for an impersonating a service account as described [here](https://cloud.google.com/iam/docs/creating-short-lived-service-account-credentials#sa-credentials-delegated).
 
 ---