func (e *EnvAWS) IsExpired() bool {
	return !e.retrieved
}
IsExpired returns if the credentials have been retrieved.
package credentials
import "os"
type EnvAWS struct {
	retrieved bool
}
func NewEnvAWS() *Credentials {
	return New(&EnvAWS{})
}
func (e *EnvAWS) Retrieve() (Value, error) {
	e.retrieved = false
	id := os.Getenv("AWS_ACCESS_KEY_ID")
	if id == "" {
		id = os.Getenv("AWS_ACCESS_KEY")
	}
	secret := os.Getenv("AWS_SECRET_ACCESS_KEY")
	if secret == "" {
		secret = os.Getenv("AWS_SECRET_KEY")
	}
	signerType := SignatureV4
	if id == "" || secret == "" {
		signerType = SignatureAnonymous
	}
	e.retrieved = true
	return Value{
		AccessKeyID:     id,
		SecretAccessKey: secret,
		SessionToken:    os.Getenv("AWS_SESSION_TOKEN"),
		SignerType:      signerType,
	}, nil
}