async _get ({ key, specOptions: { keyVaultName } }) {
    const client = this._keyvaultClient({ keyVaultName })
    this._logger.info(`fetching secret ${key} from Azure KeyVault ${keyVaultName}`)
    const secret = await client.getSecret(key)
    return secret.value
  }
Get secret property value from Azure Key Vault.
@param {string} key - Key used to store secret property value in Azure Key Vault.
@param {string} specOptions.keyVaultName - Name of the azure key vault
@returns {Promise} Promise object representing secret property value.