[GH-1275] Support for AWS access via IAMs AssumeRole functionality

This commit enables terraform to utilise the assume role functionality
of sts to execute commands with different privileges than the API
keys specified.

Signed-off-by: Ian Duffy <ian@ianduffy.ie>

builtin/providers/aws/auth_helpers.go

@@ -11,12 +11,14 @@ import (
 	"github.com/aws/aws-sdk-go/aws/awserr"
 	awsCredentials "github.com/aws/aws-sdk-go/aws/credentials"
 	"github.com/aws/aws-sdk-go/aws/credentials/ec2rolecreds"
+	"github.com/aws/aws-sdk-go/aws/credentials/stscreds"
 	"github.com/aws/aws-sdk-go/aws/ec2metadata"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/iam"
 	"github.com/aws/aws-sdk-go/service/sts"
 	"github.com/hashicorp/errwrap"
 	"github.com/hashicorp/go-cleanhttp"
+	"github.com/hashicorp/go-multierror"
 )
 
 func GetAccountId(iamconn *iam.IAM, stsconn *sts.STS, authProviderName string) (string, error) {
@@ -92,7 +94,9 @@ func parseAccountIdFromArn(arn string) (string, error) {
 // This function is responsible for reading credentials from the
 // environment in the case that they're not explicitly specified
 // in the Terraform configuration.
-func GetCredentials(c *Config) *awsCredentials.Credentials {
+func GetCredentials(c *Config) (*awsCredentials.Credentials, error) {
+	var errs []error
+
 	// build a chain provider, lazy-evaulated by aws-sdk
 	providers := []awsCredentials.Provider{
 		&awsCredentials.StaticProvider{Value: awsCredentials.Value{
@@ -137,7 +141,40 @@ func GetCredentials(c *Config) *awsCredentials.Credentials {
 		}
 	}
 
-	return awsCredentials.NewChainCredentials(providers)
+	if c.RoleArn != "" {
+		log.Printf("[INFO] attempting to assume role %s", c.RoleArn)
+
+		creds := awsCredentials.NewChainCredentials(providers)
+		cp, err := creds.Get()
+		if err != nil {
+			if awsErr, ok := err.(awserr.Error); ok && awsErr.Code() == "NoCredentialProviders" {
+				errs = append(errs, fmt.Errorf(`No valid credential sources found for AWS Provider.
+  Please see https://terraform.io/docs/providers/aws/index.html for more information on
+  providing credentials for the AWS Provider`))
+			} else {
+				errs = append(errs, fmt.Errorf("Error loading credentials for AWS Provider: %s", err))
+			}
+			return nil, &multierror.Error{Errors: errs}
+		}
+
+		log.Printf("[INFO] AWS Auth provider used: %q", cp.ProviderName)
+
+		awsConfig := &aws.Config{
+			Credentials:      creds,
+			Region:           aws.String(c.Region),
+			MaxRetries:       aws.Int(c.MaxRetries),
+			HTTPClient:       cleanhttp.DefaultClient(),
+			S3ForcePathStyle: aws.Bool(c.S3ForcePathStyle),
+		}
+
+		stsclient := sts.New(session.New(awsConfig))
+		providers = []awsCredentials.Provider{&stscreds.AssumeRoleProvider{
+			Client:  stsclient,
+			RoleARN: c.RoleArn,
+		}}
+	}
+
+	return awsCredentials.NewChainCredentials(providers), nil
 }
 
 func setOptionalEndpoint(cfg *aws.Config) string {

builtin/providers/aws/auth_helpers_test.go

@@ -218,8 +218,13 @@ func TestAWSGetCredentials_shouldError(t *testing.T) {
 	defer resetEnv()
 	cfg := Config{}
 
-	c := GetCredentials(&cfg)
-	_, err := c.Get()
+	c, err := GetCredentials(&cfg)
+	if awsErr, ok := err.(awserr.Error); ok {
+		if awsErr.Code() != "NoCredentialProviders" {
+			t.Fatalf("Expected NoCredentialProviders error")
+		}
+	}
+	_, err = c.Get()
 	if awsErr, ok := err.(awserr.Error); ok {
 		if awsErr.Code() != "NoCredentialProviders" {
 			t.Fatalf("Expected NoCredentialProviders error")
@@ -251,10 +256,13 @@ func TestAWSGetCredentials_shouldBeStatic(t *testing.T) {
 			Token:     c.Token,
 		}
 
-		creds := GetCredentials(&cfg)
+		creds, err := GetCredentials(&cfg)
 		if creds == nil {
 			t.Fatalf("Expected a static creds provider to be returned")
 		}
+		if err != nil {
+			t.Fatalf("Error gettings creds: %s", err)
+		}
 		v, err := creds.Get()
 		if err != nil {
 			t.Fatalf("Error gettings creds: %s", err)
@@ -286,11 +294,13 @@ func TestAWSGetCredentials_shouldIAM(t *testing.T) {
 	// An empty config, no key supplied
 	cfg := Config{}
 
-	creds := GetCredentials(&cfg)
+	creds, err := GetCredentials(&cfg)
 	if creds == nil {
 		t.Fatalf("Expected a static creds provider to be returned")
 	}
-
+	if err != nil {
+		t.Fatalf("Error gettings creds: %s", err)
+	}
 	v, err := creds.Get()
 	if err != nil {
 		t.Fatalf("Error gettings creds: %s", err)
@@ -335,10 +345,13 @@ func TestAWSGetCredentials_shouldIgnoreIAM(t *testing.T) {
 			Token:     c.Token,
 		}
 
-		creds := GetCredentials(&cfg)
+		creds, err := GetCredentials(&cfg)
 		if creds == nil {
 			t.Fatalf("Expected a static creds provider to be returned")
 		}
+		if err != nil {
+			t.Fatalf("Error gettings creds: %s", err)
+		}
 		v, err := creds.Get()
 		if err != nil {
 			t.Fatalf("Error gettings creds: %s", err)
@@ -362,7 +375,10 @@ func TestAWSGetCredentials_shouldErrorWithInvalidEndpoint(t *testing.T) {
 	ts := invalidAwsEnv(t)
 	defer ts()
 
-	creds := GetCredentials(&Config{})
+	creds, err := GetCredentials(&Config{})
+	if err != nil {
+		t.Fatalf("Error gettings creds: %s", err)
+	}
 	v, err := creds.Get()
 	if err == nil {
 		t.Fatal("Expected error returned when getting creds w/ invalid EC2 endpoint")
@@ -380,7 +396,10 @@ func TestAWSGetCredentials_shouldIgnoreInvalidEndpoint(t *testing.T) {
 	ts := invalidAwsEnv(t)
 	defer ts()
 
-	creds := GetCredentials(&Config{AccessKey: "accessKey", SecretKey: "secretKey"})
+	creds, err := GetCredentials(&Config{AccessKey: "accessKey", SecretKey: "secretKey"})
+	if err != nil {
+		t.Fatalf("Error gettings creds: %s", err)
+	}
 	v, err := creds.Get()
 	if err != nil {
 		t.Fatalf("Getting static credentials w/ invalid EC2 endpoint failed: %s", err)
@@ -406,10 +425,13 @@ func TestAWSGetCredentials_shouldCatchEC2RoleProvider(t *testing.T) {
 	ts := awsEnv(t)
 	defer ts()
 
-	creds := GetCredentials(&Config{})
+	creds, err := GetCredentials(&Config{})
 	if creds == nil {
 		t.Fatalf("Expected an EC2Role creds provider to be returned")
 	}
+	if err != nil {
+		t.Fatalf("Error gettings creds: %s", err)
+	}
 	v, err := creds.Get()
 	if err != nil {
 		t.Fatalf("Expected no error when getting creds: %s", err)
@@ -452,10 +474,13 @@ func TestAWSGetCredentials_shouldBeShared(t *testing.T) {
 		t.Fatalf("Error resetting env var AWS_SHARED_CREDENTIALS_FILE: %s", err)
 	}
 
-	creds := GetCredentials(&Config{Profile: "myprofile", CredsFilename: file.Name()})
+	creds, err := GetCredentials(&Config{Profile: "myprofile", CredsFilename: file.Name()})
 	if creds == nil {
 		t.Fatalf("Expected a provider chain to be returned")
 	}
+	if err != nil {
+		t.Fatalf("Error gettings creds: %s", err)
+	}
 	v, err := creds.Get()
 	if err != nil {
 		t.Fatalf("Error gettings creds: %s", err)
@@ -479,10 +504,13 @@ func TestAWSGetCredentials_shouldBeENV(t *testing.T) {
 	defer resetEnv()
 
 	cfg := Config{}
-	creds := GetCredentials(&cfg)
+	creds, err := GetCredentials(&cfg)
 	if creds == nil {
 		t.Fatalf("Expected a static creds provider to be returned")
 	}
+	if err != nil {
+		t.Fatalf("Error gettings creds: %s", err)
+	}
 	v, err := creds.Get()
 	if err != nil {
 		t.Fatalf("Error gettings creds: %s", err)

builtin/providers/aws/config.go

@@ -66,6 +66,7 @@ type Config struct {
 	Profile       string
 	Token         string
 	Region        string
+	RoleArn       string
 	MaxRetries    int
 
 	AllowedAccountIds   []interface{}
@@ -150,7 +151,10 @@ func (c *Config) Client() (interface{}, error) {
 		client.region = c.Region
 
 		log.Println("[INFO] Building AWS auth structure")
-		creds := GetCredentials(c)
+		creds, err := GetCredentials(c)
+		if err != nil {
+			return nil, &multierror.Error{Errors: errs}
+		}
 		// Call Get to check for credential provider. If nothing found, we'll get an
 		// error, and we can present it nicely to the user
 		cp, err := creds.Get()

builtin/providers/aws/provider.go

@@ -64,6 +64,13 @@ func Provider() terraform.ResourceProvider {
 				InputDefault: "us-east-1",
 			},
 
+			"role_arn": &schema.Schema{
+				Type:        schema.TypeString,
+				Optional:    true,
+				Default:     "",
+				Description: descriptions["role_arn"],
+			},
+
 			"max_retries": &schema.Schema{
 				Type:        schema.TypeInt,
 				Optional:    true,
@@ -353,6 +360,8 @@ func init() {
 		"profile": "The profile for API operations. If not set, the default profile\n" +
 			"created with `aws configure` will be used.",
 
+		"role_arn": "The role to be assumed using the supplied access_key and secret_key",
+
 		"shared_credentials_file": "The path to the shared credentials file. If not set\n" +
 			"this defaults to ~/.aws/credentials.",
 
@@ -404,6 +413,7 @@ func providerConfigure(d *schema.ResourceData) (interface{}, error) {
 		CredsFilename:           d.Get("shared_credentials_file").(string),
 		Token:                   d.Get("token").(string),
 		Region:                  d.Get("region").(string),
+		RoleArn:                 d.Get("role_arn").(string),
 		MaxRetries:              d.Get("max_retries").(int),
 		DynamoDBEndpoint:        d.Get("dynamodb_endpoint").(string),
 		KinesisEndpoint:         d.Get("kinesis_endpoint").(string),

state/remote/s3.go

@@ -60,7 +60,7 @@ func s3Factory(conf map[string]string) (Client, error) {
 	kmsKeyID := conf["kms_key_id"]
 
 	var errs []error
-	creds := terraformAws.GetCredentials(&terraformAws.Config{
+	creds, err := terraformAws.GetCredentials(&terraformAws.Config{
 		AccessKey:     conf["access_key"],
 		SecretKey:     conf["secret_key"],
 		Token:         conf["token"],
@@ -69,7 +69,7 @@ func s3Factory(conf map[string]string) (Client, error) {
 	})
 	// Call Get to check for credential provider. If nothing found, we'll get an
 	// error, and we can present it nicely to the user
-	_, err := creds.Get()
+	_, err = creds.Get()
 	if err != nil {
 		if awsErr, ok := err.(awserr.Error); ok && awsErr.Code() == "NoCredentialProviders" {
 			errs = append(errs, fmt.Errorf(`No valid credential sources found for AWS S3 remote.

website/source/docs/providers/aws/index.html.markdown

@@ -111,6 +111,19 @@ You can provide custom metadata API endpoint via `AWS_METADATA_ENDPOINT` variabl
 which expects the endpoint URL including the version
 and defaults to `http://169.254.169.254:80/latest`.
 
+###Assume role
+
+If provided with a role arn, terraform will attempt to assume this role
+using the supplied credentials.
+
+Usage:
+
+```
+provider "aws" {
+  role_arn = "arn:aws:iam::ACCOUNT_ID:role/ROLE_NAME"
+}
+```
+
 ## Argument Reference
 
 The following arguments are supported in the `provider` block: