code: func NewAuthFromEnv() (Auth, error) {
  	accessKey := os.Getenv(AccessEnvKey)
  	if accessKey == "" {
  		accessKey = os.Getenv(AccessEnvKeyId)
  	}
  
  	secretKey := os.Getenv(SecretEnvKey)
  	if secretKey == "" {
  		secretKey = os.Getenv(SecretEnvAccessKey)
  	}
  
  	token := os.Getenv(SecurityTokenEnvKey)
  
  	if accessKey == "" && secretKey == "" && token == "" {
  		return nil, fmt.Errorf("No access key (%s or %s), secret key (%s or %s), or security token (%s) env variables were set", AccessEnvKey, AccessEnvKeyId, SecretEnvKey, SecretEnvAccessKey, SecurityTokenEnvKey)
  	}
  	if accessKey == "" {
  		return nil, fmt.Errorf("Unable to retrieve access key from %s or %s env variables", AccessEnvKey, AccessEnvKeyId)
  	}
  	if secretKey == "" {
  		return nil, fmt.Errorf("Unable to retrieve secret key from %s or %s env variables", SecretEnvKey, SecretEnvAccessKey)
  	}
  
  	return NewAuth(accessKey, secretKey, token), nil
  }
docs: // NewAuthFromEnv retrieves auth credentials from environment vars