Add AWS_SESSION_TOKEN into aws.Config to allow using temporary credentials (#154)

* Add AWS_SESSION_TOKEN to allow using temp credentials

Currently, using temp credentials is only possible via environment.
If one requires to configure the client in code, there is no way
to specify session token.

* Update NewPublisher to make use of session token

Subscriber constructor was modified to make use of newly added
SessionToken field in the config.
The publisher was missed out. Fixing this injustice...

Author: avepr

config/aws/aws.go

@@ -22,11 +22,12 @@ const (
 type (
 	// Config holds common AWS credentials and keys.
 	Config struct {
-		AccessKey string `envconfig:"AWS_ACCESS_KEY"`
+		AccessKey       string `envconfig:"AWS_ACCESS_KEY"`
 		MFASerialNumber string `envconfig:"AWS_MFA_SERIAL_NUMBER"`
-		Region string `envconfig:"AWS_REGION"`
-		RoleARN string `envconfig:"AWS_ROLE_ARN"`
-		SecretKey string `envconfig:"AWS_SECRET_KEY"`
+		Region          string `envconfig:"AWS_REGION"`
+		RoleARN         string `envconfig:"AWS_ROLE_ARN"`
+		SecretKey       string `envconfig:"AWS_SECRET_KEY"`
+		SessionToken    string `envconfig:"AWS_SESSION_TOKEN"`
 	}
 
 	// S3 holds the info required to work with Amazon S3.

pubsub/aws/aws.go

@@ -45,7 +45,7 @@ func NewPublisher(cfg SNSConfig) (pubsub.Publisher, error) {
 
 	var creds *credentials.Credentials
 	if cfg.AccessKey != "" {
-		creds = credentials.NewStaticCredentials(cfg.AccessKey, cfg.SecretKey, "")
+		creds = credentials.NewStaticCredentials(cfg.AccessKey, cfg.SecretKey, cfg.SessionToken)
 	} else {
 		creds = credentials.NewEnvCredentials()
 	}
@@ -202,7 +202,7 @@ func NewSubscriber(cfg SQSConfig) (pubsub.Subscriber, error) {
 
 	var creds *credentials.Credentials
 	if cfg.AccessKey != "" {
-		creds = credentials.NewStaticCredentials(cfg.AccessKey, cfg.SecretKey, "")
+		creds = credentials.NewStaticCredentials(cfg.AccessKey, cfg.SecretKey, cfg.SessionToken)
 	} else {
 		creds = credentials.NewEnvCredentials()
 	}