Attempts to authenticate against the mongo instance.

    Tries:
      - Auth'ing against admin as 'admin' ; credentials: <host>/arctic/admin/admin
      - Auth'ing against db_name (which may be None if auth'ing against admin above)

    returns True if authentication succeeded.

def do_db_auth(host, connection, db_name):
    """
    Attempts to authenticate against the mongo instance.

    Tries:
      - Auth'ing against admin as 'admin' ; credentials: <host>/arctic/admin/admin
      - Auth'ing against db_name (which may be None if auth'ing against admin above)

    returns True if authentication succeeded.
    """
    admin_creds = get_auth(host, 'admin', 'admin')
    user_creds = get_auth(host, 'arctic', db_name)

    # Attempt to authenticate the connection
    # Try at 'admin level' first as this allows us to enableSharding, which we want
    if admin_creds is None:
        # Get ordinary credentials for authenticating against the DB
        if user_creds is None:
            logger.error("You need credentials for db '%s' on '%s', or admin credentials" % (db_name, host))
            return False
        if not authenticate(connection[db_name], user_creds.user, user_creds.password):
            logger.error("Failed to authenticate to db '%s' on '%s', using user credentials" % (db_name, host))
            return False
        return True
    elif not authenticate(connection.admin, admin_creds.user, admin_creds.password):
        logger.error("Failed to authenticate to '%s' as Admin. Giving up." % (host))
        return False
    # Ensure we attempt to auth against the user DB, for non-priviledged users to get access
    authenticate(connection[db_name], user_creds.user, user_creds.password)
    return True