def role_ids_for_account(dynamo_table, account_number):
    """
    Get a list of all role IDs in a given account by querying the Dynamo secondary index 'account'

    Args:
        account_number (string)

    Returns:
        list: role ids in given account
    """
    role_ids = set()

    results = dynamo_table.query(IndexName='Account',
                                 KeyConditionExpression='Account = :act',
                                 ExpressionAttributeValues={':act': account_number})
    role_ids.update([return_dict['RoleId'] for return_dict in results.get('Items')])

    while 'LastEvaluatedKey' in results:
        results = dynamo_table.query(IndexName='Account',
                                     KeyConditionExpression='Account = :act',
                                     ExpressionAttributeValues={':act': account_number},
                                     ExclusiveStartKey=results.get('LastEvaluatedKey'))
        role_ids.update([return_dict['RoleId'] for return_dict in results.get('Items')])
    return role_ids