provider/aws: Allow account ID checks on EC2 instances & w/ federated accounts

builtin/providers/aws/auth_helpers.go

@@ -0,0 +1,134 @@
+package aws
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"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/ec2metadata"
+	"github.com/aws/aws-sdk-go/aws/session"
+	"github.com/aws/aws-sdk-go/service/iam"
+	"github.com/hashicorp/go-cleanhttp"
+)
+
+func GetAccountId(iamconn *iam.IAM, authProviderName string) (string, error) {
+	// If we have creds from instance profile, we can use metadata API
+	if authProviderName == ec2rolecreds.ProviderName {
+		log.Println("[DEBUG] Trying to get account ID via AWS Metadata API")
+
+		cfg := &aws.Config{}
+		setOptionalEndpoint(cfg)
+		metadataClient := ec2metadata.New(session.New(cfg))
+		info, err := metadataClient.IAMInfo()
+		if err != nil {
+			// This can be triggered when no IAM Role is assigned
+			// or AWS just happens to return invalid response
+			return "", fmt.Errorf("Failed getting EC2 IAM info: %s", err)
+		}
+
+		return parseAccountIdFromArn(info.InstanceProfileArn)
+	}
+
+	// Then try IAM GetUser
+	log.Println("[DEBUG] Trying to get account ID via iam:GetUser")
+	outUser, err := iamconn.GetUser(nil)
+	if err == nil {
+		return parseAccountIdFromArn(*outUser.User.Arn)
+	}
+
+	// Then try IAM ListRoles
+	awsErr, ok := err.(awserr.Error)
+	// AccessDenied and ValidationError can be raised
+	// if credentials belong to federated profile, so we ignore these
+	if !ok || (awsErr.Code() != "AccessDenied" && awsErr.Code() != "ValidationError") {
+		return "", fmt.Errorf("Failed getting account ID via 'iam:GetUser': %s", err)
+	}
+
+	log.Printf("[DEBUG] Getting account ID via iam:GetUser failed: %s", err)
+	log.Println("[DEBUG] Trying to get account ID via iam:ListRoles instead")
+	outRoles, err := iamconn.ListRoles(&iam.ListRolesInput{
+		MaxItems: aws.Int64(int64(1)),
+	})
+	if err != nil {
+		return "", fmt.Errorf("Failed getting account ID via 'iam:ListRoles': %s", err)
+	}
+
+	if len(outRoles.Roles) < 1 {
+		return "", fmt.Errorf("Failed getting account ID via 'iam:ListRoles': No roles available")
+	}
+
+	return parseAccountIdFromArn(*outRoles.Roles[0].Arn)
+}
+
+func parseAccountIdFromArn(arn string) (string, error) {
+	parts := strings.Split(arn, ":")
+	if len(parts) < 5 {
+		return "", fmt.Errorf("Unable to parse ID from invalid ARN: %q", arn)
+	}
+	return parts[4], nil
+}
+
+// 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(key, secret, token, profile, credsfile string) *awsCredentials.Credentials {
+	// build a chain provider, lazy-evaulated by aws-sdk
+	providers := []awsCredentials.Provider{
+		&awsCredentials.StaticProvider{Value: awsCredentials.Value{
+			AccessKeyID:     key,
+			SecretAccessKey: secret,
+			SessionToken:    token,
+		}},
+		&awsCredentials.EnvProvider{},
+		&awsCredentials.SharedCredentialsProvider{
+			Filename: credsfile,
+			Profile:  profile,
+		},
+	}
+
+	// Build isolated HTTP client to avoid issues with globally-shared settings
+	client := cleanhttp.DefaultClient()
+
+	// Keep the timeout low as we don't want to wait in non-EC2 environments
+	client.Timeout = 100 * time.Millisecond
+	cfg := &aws.Config{
+		HTTPClient: client,
+	}
+	usedEndpoint := setOptionalEndpoint(cfg)
+
+	// Real AWS should reply to a simple metadata request.
+	// We check it actually does to ensure something else didn't just
+	// happen to be listening on the same IP:Port
+	metadataClient := ec2metadata.New(session.New(cfg))
+	if metadataClient.Available() {
+		providers = append(providers, &ec2rolecreds.EC2RoleProvider{
+			Client: metadataClient,
+		})
+		log.Printf("[INFO] AWS EC2 instance detected via default metadata" +
+			" API endpoint, EC2RoleProvider added to the auth chain")
+	} else {
+		if usedEndpoint == "" {
+			usedEndpoint = "default location"
+		}
+		log.Printf("[WARN] Ignoring AWS metadata API endpoint at %s "+
+			"as it doesn't return any instance-id", usedEndpoint)
+	}
+
+	return awsCredentials.NewChainCredentials(providers)
+}
+
+func setOptionalEndpoint(cfg *aws.Config) string {
+	endpoint := os.Getenv("AWS_METADATA_URL")
+	if endpoint != "" {
+		log.Printf("[INFO] Setting custom metadata endpoint: %q", endpoint)
+		cfg.Endpoint = aws.String(endpoint)
+		return endpoint
+	}
+	return ""
+}