__savePreLoginAccount = async preLoginItem => {
  console.log(
    'Saving pre-login account data:',
    JSON.stringify(preLoginItem, null, 2)
  )

  try {
    await dynamoDb
      .put({
        TableName: getEnv('PreLoginAccountsTableName'),
        Item: preLoginItem,
        ConditionExpression: 'attribute_not_exists(UserId)'
      })
      .promise()
  } catch (error) {
    console.error(
      'Failed to add save pre-login account data for' +
      ` userId=[${preLoginItem.UserId}]:`,
      error
    )
    throw error
  }
  return preLoginItem
}
Creates an item in the PreLoginAccountsTable for the given `preLoginItem`'s
`UserId`.