InternetExplorer.Application, click checkbox and PowerShell - powershell

Question

I am having an issue with selecting a checkbox. I have been able to successfully login and navigate via the ID tags, but this one doesn't have one. The only tags it has is type and class.
I can find this section using $ie.document.IHTMLDocument3_getElementByTagName("input"), but I can't find any way to utilize it.
Here's the html I'm working with:
<th class="cText sorting_disabled cHeader" rowspan="1" colspan="1" style="width: 5px;" aria-label="">
<input type="checkbox" class="selectall">
</th>
What I have thus far:
$ie = New-Object -ComObject "InternetExplorer.Application"
$ie.visible = "true"
$ie.navigate("https://some.site.com")
while($ie.Busy) { Start-Sleep -Milliseconds 100 }
# login
$usernameField = $ie.document.IHTMLDocument3_getElementByID("userid")
$passwordField = $ie.document.IHTMLDocument3_getElementByID("Password")
$usernameField.value = "email#domain.com"
$passwordField.value = "supercoolpassword"
$btn_Submit = $ie.document.IHTMLDocument3_getElementByID("btn_signIn")
$btn_Submit.click()
# go to downloads page
$ie.navigate("https://some.site.com/pages/mydownloads.aspx")
# selectall packages to download has me clueless
When the checkbox is clicked the result should be all checkboxes should be ticked.

Answer 1

This is common place, so, you have to approach this differently.
$SiteSource.AllElements | Where{$_.TagName -eq 'input'}
or, like if it were a button
($ie.Document.IHTMLDocument3_getElementsByTagName('button') |
Where-Object innerText -eq 'SIGN IN').Click()
But how are you walking the site to get the needed objects?
An approach I regularly use before making coding decisions.
$SiteSource = Invoke-WebRequest -Uri 'SomeUrl'
# single form site
$SiteSource.Forms | Format-List -Force
# multi-form sites
$SiteSource.Forms[0] | Format-List -Force
$SiteSource.Forms[1] | Format-List -Force
# Check for what can be used.
$SiteSource.Forms.Fields
$SiteSource.InputFields
Then once gathering the above... code for what can be found and used.
$ie = New-Object -com InternetExplorer.Application
$ie.visible=$true
$ie.navigate('SomeUrl')
while($ie.ReadyState -ne 4) {start-sleep -m 100}
$UserID = $ie.document.getElementsByTagName('INPUT') |
Where-Object {$($_.Name) -match 'userid'}
$UserId.value = 'UserID'
$UserPassword = $ie.document.getElementsByTagName('INPUT') |
Where-Object {$($_.Name) -match 'password'}
$UserPassword.value = 'password'
$Submit = $ie.document.getElementsByTagName('INPUT') |
Where-Object {$($_.Value) -match 'SomeString'}
$Submit.click()