def _nens_user_extract_username(claims):
    """Return the username from the email claim if the user is a N&S user.

    A N&S user is characterized by 1) coming from either "Google" or
    "NelenSchuurmans" identity provider and 2) having (verified)
    email domain @nelen-schuurmans.nl.
    """
    # Get the provider name, return False if not present
    try:
        provider_name = claims["identities"][0]["providerName"]
    except (KeyError, IndexError):
        return

    if provider_name not in ("Google", "NelenSchuurmans"):
        return
    if not claims.get("email_verified", False):
        return

    # Unpack email
    username, domain = claims.get("email", "a@b").split("@", 1)
    if domain != "nelen-schuurmans.nl":
        return

    return username