_secretsManagerClient () {
    let authenticator
    if (process.env.IBM_CLOUD_SECRETS_MANAGER_API_AUTH_TYPE) {
      authenticator = getAuthenticatorFromEnvironment('IBM_CLOUD_SECRETS_MANAGER_API')
    } else {
      authenticator = new IamAuthenticator({
        apikey: this._credential.apikey
      })
    }
    const client = new SecretsManager({
      authenticator: authenticator,
      serviceUrl: this._credential.endpoint
    })
    return client
  }
Create Key Vault backend.
@param {Object} credential - Credentials for authenticating with IBM Secrets Manager.
@param {Object} logger - Logger for logging stuff.