Direct passing WebIdentity token to AWS provider

pkg/aws/aws.go

@@ -42,6 +42,9 @@ const (
 	// "config". It is optional.
 	ConfigEFSVaultName = "efsVaultName"
 
+	// ConfigWebIdentityToken represents the key for AWS Web Identity token
+	ConfigWebIdentityToken = "webIdentityToken"
+
 	// AccessKeyID represents AWS Access key ID
 	AccessKeyID = "AWS_ACCESS_KEY_ID"
 	// SecretAccessKey represents AWS Secret Access Key
@@ -60,6 +63,17 @@ const (
 	AssumeRoleDuration        = "assumeRoleDuration"
 )
 
+var _ stscreds.TokenFetcher = (*staticToken)(nil)
+
+// staticToken implements stscreds.TokenFetcher interface for retrieval of plaintext web
+// identity token
+type staticToken string
+
+// FetchToken returns a plaintext web identity token as is.
+func (f staticToken) FetchToken(ctx credentials.Context) ([]byte, error) {
+	return []byte(f), nil
+}
+
 func durationFromString(config map[string]string) (time.Duration, error) {
 	d, ok := config[AssumeRoleDuration]
 	if !ok || d == "" {
@@ -68,25 +82,78 @@ func durationFromString(config map[string]string) (time.Duration, error) {
 	return time.ParseDuration(d)
 }
 
-func authenticateAWSCredentials(ctx context.Context, config map[string]string, assumeRoleDuration time.Duration) (*credentials.Credentials, string, error) {
-	var creds *credentials.Credentials
-	var assumedRole string
-
-	switch {
-	case config[AccessKeyID] != "" && config[SecretAccessKey] != "":
-		// If AccessKeys were provided - use those
-		creds = credentials.NewStaticCredentials(config[AccessKeyID], config[SecretAccessKey], "")
-	case os.Getenv(webIdentityTokenFilePathEnvKey) != "" && os.Getenv(roleARNEnvKey) != "":
-		sess, err := session.NewSessionWithOptions(session.Options{AssumeRoleDuration: assumeRoleDuration})
-		if err != nil {
-			return nil, "", errors.Wrap(err, "Failed to create session to initialize Web Identify credentials")
-		}
-		creds = getCredentialsWithDuration(sess, assumeRoleDuration)
-		assumedRole = os.Getenv(roleARNEnvKey)
-	default:
-		return nil, "", errors.New("AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY required to initialize AWS credentials")
-	}
-	return creds, assumedRole, nil
+func authenticateAWSCredentials(
+	config map[string]string,
+	assumeRoleDuration time.Duration,
+) (*credentials.Credentials, string, error) {
+	// If AccessKeys were provided - use those
+	creds := fetchStaticAWSCredentials(config)
+	if creds != nil {
+		return creds, "", nil
+	}
+
+	// If Web Identity token and role were provided - use them
+	var err error
+	creds, err = fetchWebIdentityTokenFromConfig(config, assumeRoleDuration)
+	if err != nil {
+		return nil, "", err
+	}
+	if creds != nil {
+		return creds, config[ConfigRole], nil
+	}
+
+	// Otherwise use Web Identity token file and role provided via ENV
+	creds, err = fetchWebIdentityTokenFromFile(assumeRoleDuration)
+	if err != nil {
+		return nil, "", err
+	}
+	if creds != nil {
+		return creds, os.Getenv(roleARNEnvKey), nil
+	}
+
+	return nil, "", errors.New("Missing AWS credentials, please check that either AWS access keys or web identity token are provided")
+}
+
+func fetchStaticAWSCredentials(config map[string]string) *credentials.Credentials {
+	if config[AccessKeyID] == "" || config[SecretAccessKey] == "" {
+		return nil
+	}
+
+	return credentials.NewStaticCredentials(config[AccessKeyID], config[SecretAccessKey], "")
+}
+
+func fetchWebIdentityTokenFromConfig(config map[string]string, assumeRoleDuration time.Duration) (*credentials.Credentials, error) {
+	if config[ConfigWebIdentityToken] == "" || config[ConfigRole] == "" {
+		return nil, nil
+	}
+
+	creds, err := getCredentialsWithDuration(
+		config[ConfigRole],
+		staticToken(config[ConfigWebIdentityToken]),
+		assumeRoleDuration,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return creds, nil
+}
+
+func fetchWebIdentityTokenFromFile(assumeRoleDuration time.Duration) (*credentials.Credentials, error) {
+	if os.Getenv(webIdentityTokenFilePathEnvKey) == "" || os.Getenv(roleARNEnvKey) == "" {
+		return nil, nil
+	}
+
+	creds, err := getCredentialsWithDuration(
+		os.Getenv(roleARNEnvKey),
+		stscreds.FetchTokenPath(os.Getenv(webIdentityTokenFilePathEnvKey)),
+		assumeRoleDuration,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return creds, nil
 }
 
 // switchAWSRole checks if the caller wants to assume a different role
@@ -116,7 +183,7 @@ func GetCredentials(ctx context.Context, config map[string]string) (*credentials
 	log.Debug().Print("Assume Role Duration setup", field.M{"assumeRoleDuration": assumeRoleDuration})
 
 	// authenticate AWS creds
-	creds, assumedRole, err := authenticateAWSCredentials(ctx, config, assumeRoleDuration)
+	creds, assumedRole, err := authenticateAWSCredentials(config, assumeRoleDuration)
 	if err != nil {
 		return nil, err
 	}
@@ -128,16 +195,25 @@ func GetCredentials(ctx context.Context, config map[string]string) (*credentials
 // In order to set a custom assume role duration, we have to get the
 // the provider first and then set it's Duration field before
 // getting the credentials from the provider.
-func getCredentialsWithDuration(sess *session.Session, duration time.Duration) *credentials.Credentials {
+func getCredentialsWithDuration(
+	roleARN string,
+	tokenFetcher stscreds.TokenFetcher,
+	duration time.Duration,
+) (*credentials.Credentials, error) {
+	sess, err := session.NewSessionWithOptions(session.Options{AssumeRoleDuration: duration})
+	if err != nil {
+		return nil, errors.Wrap(err, "Failed to create session to initialize Web Identify credentials")
+	}
+
 	svc := sts.New(sess)
 	p := stscreds.NewWebIdentityRoleProviderWithOptions(
 		svc,
-		os.Getenv(roleARNEnvKey),
+		roleARN,
 		"",
-		stscreds.FetchTokenPath(os.Getenv(webIdentityTokenFilePathEnvKey)),
+		tokenFetcher,
 	)
 	p.Duration = duration
-	return credentials.NewCredentials(p)
+	return credentials.NewCredentials(p), nil
 }
 
 // GetConfig returns a configuration to establish AWS connection and connected region name.