[SM9]

PHP Code:

char chRestrictedIds[][] = 
{
    "",
    "STEAM_ID_LAN",
    "STEAM_ID_VALVE",
    "VALVE_ID_LAN",
    "STEAM_1:0:0",
    "STEAM_0:0:0",
    "[I:0:0]",
    
};

public Plugin:myinfo = 
{
    name = "Null Auth Ban",
    author = "SM9 (xCoderx)",
}

public void OnClientAuthorized(int iClient, const char[] chAuthId)
{
    char chAuthId2[30], chAuthId3[30]
    
    GetClientAuthId(iClient, AuthId_Steam2, chAuthId2, sizeof(chAuthId2))
    GetClientAuthId(iClient, AuthId_Steam3, chAuthId3, sizeof(chAuthId3))
    
    for(int i; i < sizeof(chRestrictedIds); i++)
    {
        if(StrEqual(chAuthId2, chRestrictedIds[i], false) || StrEqual(chAuthId3, chRestrictedIds[i], false) || StrEqual(chAuthId, chRestrictedIds[i], false))
        {
            BanClient(iClient, 0, BANFLAG_IP, "Null / Invalid AuthId (%s)", "Null / Invalid AuthId");
            if(IsClientInGame(iClient)) KickClient(iClient, "Null / Invalid AuthId");
            break;
        }
        
        continue;
    }
    
    if(!IsClientAuthorized(iClient)) KickClient(iClient, "Authorize failure, please retry.");
} 


Try this, you can add your own ids to the top aswell.