auth_helpers.go

package aws

import (
	"errors"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/arn"
	"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/defaults"
	"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) {
	var errors 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)
		sess, err := session.NewSession(cfg)
		if err != nil {
			return "", errwrap.Wrapf("Error creating AWS session: {{err}}", err)
		}

		metadataClient := ec2metadata.New(sess)
		info, err := metadataClient.IAMInfo()
		if err == nil {
			return parseAccountIDFromArn(info.InstanceProfileArn)
		}
		log.Printf("[DEBUG] Failed to get account info from metadata service: %s", err)
		errors = multierror.Append(errors, err)
		// We can end up here if there's an issue with the instance metadata service
		// or if we're getting credentials from AdRoll's Hologram (in which case IAMInfo will
		// error out). In any event, if we can't get account info here, we should try
		// the other methods available.
		// If we have creds from something that looks like an IAM instance profile, but
		// we were unable to retrieve account info from the instance profile, it's probably
		// a safe assumption that we're not an IAM user
	} else {
		// Creds aren't from an IAM instance profile, so try 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)
		}
		errors = multierror.Append(errors, err)
		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" && awsErr.Code() != "InvalidClientTokenId") {
			return "", fmt.Errorf("Failed getting account ID via 'iam:GetUser': %s", err)
		}
		log.Printf("[DEBUG] Getting account ID via iam:GetUser failed: %s", err)
	}

	// Then try STS GetCallerIdentity
	log.Println("[DEBUG] Trying to get account ID via sts:GetCallerIdentity")
	outCallerIdentity, err := stsconn.GetCallerIdentity(&sts.GetCallerIdentityInput{})
	if err == nil {
		return parseAccountIDFromArn(*outCallerIdentity.Arn)
	}
	log.Printf("[DEBUG] Getting account ID via sts:GetCallerIdentity failed: %s", err)
	errors = multierror.Append(errors, err)

	// Then try IAM ListRoles
	log.Println("[DEBUG] Trying to get account ID via iam:ListRoles")
	outRoles, err := iamconn.ListRoles(&iam.ListRolesInput{
		MaxItems: aws.Int64(int64(1)),
	})
	if err != nil {
		log.Printf("[DEBUG] Failed to get account ID via iam:ListRoles: %s", err)
		errors = multierror.Append(errors, err)
		return "", fmt.Errorf("Failed getting account ID via all available methods. Errors: %s", errors)
	}

	if len(outRoles.Roles) < 1 {
		err = fmt.Errorf("Failed to get account ID via iam:ListRoles: No roles available")
		log.Printf("[DEBUG] %s", err)
		errors = multierror.Append(errors, err)
		return "", fmt.Errorf("Failed getting account ID via all available methods. Errors: %s", errors)
	}

	return parseAccountIDFromArn(*outRoles.Roles[0].Arn)
}

func parseAccountIDFromArn(inputARN string) (string, error) {
	arn, err := arn.Parse(inputARN)
	if err != nil {
		return "", fmt.Errorf("Unable to parse ID from invalid ARN: %q", arn)
	}
	return arn.AccountID, 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(c *Config) (*awsCredentials.Credentials, error) {
	// build a chain provider, lazy-evaluated by aws-sdk
	providers := []awsCredentials.Provider{
		&awsCredentials.StaticProvider{Value: awsCredentials.Value{
			AccessKeyID:     c.AccessKey,
			SecretAccessKey: c.SecretKey,
			SessionToken:    c.Token,
		}},
		&awsCredentials.EnvProvider{},
		&awsCredentials.SharedCredentialsProvider{
			Filename: c.CredsFilename,
			Profile:  c.Profile,
		},
	}

	// Build isolated HTTP client to avoid issues with globally-shared settings
	client := cleanhttp.DefaultClient()

	// Keep the default timeout (100ms) low as we don't want to wait in non-EC2 environments
	client.Timeout = 100 * time.Millisecond

	const userTimeoutEnvVar = "AWS_METADATA_TIMEOUT"
	userTimeout := os.Getenv(userTimeoutEnvVar)
	if userTimeout != "" {
		newTimeout, err := time.ParseDuration(userTimeout)
		if err == nil {
			if newTimeout.Nanoseconds() > 0 {
				client.Timeout = newTimeout
			} else {
				log.Printf("[WARN] Non-positive value of %s (%s) is meaningless, ignoring", userTimeoutEnvVar, newTimeout.String())
			}
		} else {
			log.Printf("[WARN] Error converting %s to time.Duration: %s", userTimeoutEnvVar, err)
		}
	}

	log.Printf("[INFO] Setting AWS metadata API timeout to %s", client.Timeout.String())
	cfg := &aws.Config{
		HTTPClient: client,
	}
	usedEndpoint := setOptionalEndpoint(cfg)

	// Add the default AWS provider for ECS Task Roles if the relevant env variable is set
	if uri := os.Getenv("AWS_CONTAINER_CREDENTIALS_RELATIVE_URI"); len(uri) > 0 {
		providers = append(providers, defaults.RemoteCredProvider(*cfg, defaults.Handlers()))
		log.Print("[INFO] ECS container credentials detected, RemoteCredProvider added to auth chain")
	}

	if !c.SkipMetadataApiCheck {
		// 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.Print("[INFO] AWS EC2 instance detected via default metadata" +
				" API endpoint, EC2RoleProvider added to the auth chain")
		} else {
			if usedEndpoint == "" {
				usedEndpoint = "default location"
			}
			log.Printf("[INFO] Ignoring AWS metadata API endpoint at %s "+
				"as it doesn't return any instance-id", usedEndpoint)
		}
	}

	// This is the "normal" flow (i.e. not assuming a role)
	if c.AssumeRoleARN == "" {
		return awsCredentials.NewChainCredentials(providers), nil
	}

	// Otherwise we need to construct and STS client with the main credentials, and verify
	// that we can assume the defined role.
	log.Printf("[INFO] Attempting to AssumeRole %s (SessionName: %q, ExternalId: %q, Policy: %q)",
		c.AssumeRoleARN, c.AssumeRoleSessionName, c.AssumeRoleExternalID, c.AssumeRolePolicy)

	creds := awsCredentials.NewChainCredentials(providers)
	cp, err := creds.Get()
	if err != nil {
		if awsErr, ok := err.(awserr.Error); ok && awsErr.Code() == "NoCredentialProviders" {
			return nil, errors.New(`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`)
		}

		return nil, fmt.Errorf("Error loading credentials for AWS Provider: %s", err)
	}

	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))
	assumeRoleProvider := &stscreds.AssumeRoleProvider{
		Client:  stsclient,
		RoleARN: c.AssumeRoleARN,
	}
	if c.AssumeRoleSessionName != "" {
		assumeRoleProvider.RoleSessionName = c.AssumeRoleSessionName
	}
	if c.AssumeRoleExternalID != "" {
		assumeRoleProvider.ExternalID = aws.String(c.AssumeRoleExternalID)
	}
	if c.AssumeRolePolicy != "" {
		assumeRoleProvider.Policy = aws.String(c.AssumeRolePolicy)
	}

	providers = []awsCredentials.Provider{assumeRoleProvider}

	assumeRoleCreds := awsCredentials.NewChainCredentials(providers)
	_, err = assumeRoleCreds.Get()
	if err != nil {
		if awsErr, ok := err.(awserr.Error); ok && awsErr.Code() == "NoCredentialProviders" {
			return nil, fmt.Errorf("The role %q cannot be assumed.\n\n"+
				"  There are a number of possible causes of this - the most common are:\n"+
				"    * The credentials used in order to assume the role are invalid\n"+
				"    * The credentials do not have appropriate permission to assume the role\n"+
				"    * The role ARN is not valid",
				c.AssumeRoleARN)
		}

		return nil, fmt.Errorf("Error loading credentials for AWS Provider: %s", err)
	}

	return assumeRoleCreds, nil
}

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 ""
}