Detect web requests to potentially harmful files (ASIM Web Session)

Original query, unchanged.

let lookback = 5m;
let RiskyFileExtensions = materialize(externaldata(Extensions: string)
    [@"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/RiskyFileExtensionsInUrl.csv"]
    with(format="csv", ignoreFirstRecord=True));
let CustomRiskyFileExtensions = (_ASIM_GetWatchlistRaw("Web_RiskyFileExtensions") // Create new Watchlist and add your custom indicators(Optional)
    | extend
        Extensions = tostring(WatchlistItem["Extensions"])
    | project Extensions
    | where isnotempty(Extensions));
let CombinedRiskyFileExtensions = union RiskyFileExtensions, CustomRiskyFileExtensions;
let knownRiskyFileExtensions=toscalar(CombinedRiskyFileExtensions
    | where isnotempty(Extensions)
    | summarize make_set(Extensions, 1000));
let Whitelisted_Domains = materialize(externaldata(WhiteListedDomains: string)
    [@"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/WhiteListedDomainsForWebSessionUseCases.csv"]
    with(format="csv", ignoreFirstRecord=True));
let CustomWhiteListedDomains = (_ASIM_GetWatchlistRaw("Web_WhiteListedDomains") // Create new Watchlist and add your white listed domains(Optional)
    | extend
        WhiteListedDomains = tostring(WatchlistItem["WhiteListedDomains"])
    | project WhiteListedDomains
    | where isnotempty(WhiteListedDomains));
let CombinedWhitelisted_Domains = union Whitelisted_Domains, CustomWhiteListedDomains;
let knownWhitelisted_Domains=toscalar(CombinedWhitelisted_Domains
    | where isnotempty(WhiteListedDomains)
    | summarize make_set(WhiteListedDomains, 1000));
_Im_WebSession (starttime=ago(lookback), url_has_any=knownRiskyFileExtensions, eventresult='Success')
| project
    Url,
    SrcIpAddr,
    TimeGenerated,
    SrcUsername,
    SrcHostname,
    DstIpAddr,
    DstPortNumber
| extend requestedFileName=tostring(split(tostring(parse_url(Url)["Path"]), '/')[-1])
| extend requestedFileExt=extract(@'(\.\w+)$', 1, requestedFileName, typeof(string))
| where requestedFileExt in~ (knownRiskyFileExtensions)
| summarize
    EventCount=count(),
    EventStartTime=min(TimeGenerated),
    EventEndTime=max(TimeGenerated)
    by
    SrcUsername,
    SrcIpAddr,
    SrcHostname,
    DstIpAddr,
    DstPortNumber,
    Url,
    requestedFileName
| extend FQDN = split(parse_url(Url)["Host"], '.')
| extend Domain = iif(array_length(FQDN) > 1, strcat(FQDN[-2], '.', FQDN[-1]), FQDN)
| where Domain !in~ (knownWhitelisted_Domains)
| project-away FQDN
| extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")