Script to download file from javascript Postback

PoSH_Postback.ps1

#URL that needs to be fetched
$url = "https://site.state.gov/default.aspx"

#get the server name in case the process jumps to another script
$serverName = $env:computername

#wrapped it into a try/catch for some type of error handling
TRY {
  #use invoke-webrequest to fetch a session from the site
  Invoke-WebRequest $url -SessionVariable session -UseBasicParsing

  #add a site using the session information from the above web request
  $addUserSite = Invoke-WebRequest $url -WebSession $session 
  $addUserForm = $addUserSite.Forms[0] #Invoke-WebRequest does a lot of auto processing. 

  #add form fields for the event target & argument that is needed to actually do the post back
  $addUserForm.Fields["__EVENTTARGET"] = "dnn`$abcd1234`$File`$ExcelFile" 
  $addUserForm.Fields["__EVENTARGUMENT"] = "" 

  #where are we saving the file & what is file name
  $filename = "C:\temp\Download_FIle_Name.txt"

  #invoke another web request using the same url, session information, and out put to the $filename variable
  Invoke-WebRequest -uri $url -method post -Body $addUserForm.Fields -WebSession $session  -UseBasicParsing -Outfile $fileName
}

# catch any errors from above and send an email to the right people
CATCH {
   Send-MailMessage -To "it@somecompany.com" -From "donotrely@somecompany.com" -Subject "Some important thing just happened" -SmtpServer "server.smtp.com" -Body "Check stuff out on $serverName"
}

In my case, I was trying to do this post back where DNN was the provider. I was able to hover over the initial link to identify what the parameters had to be set to. I believe if you look at the HTML of the form/page itself there's a form the page that will identify the parameters as well.