$ie = New-Object -ComObject 'internetExplorer.Application'
$ie.Visible= $true
$username="username@domain.com"
$password="password"
$ie.Navigate("https://www.yourwebsite.com")
While ($ie.Busy -eq $true)
{
Start-Sleep -Seconds 3
}
$usernamefield = $ie.document.getElementByID('Email_ID').value="$username"
$passwordfield = $ie.document.getElementByID('Password').value="$password"
$Link = $ie.document.getElementByID('Login_ID')
$Link.click() #or $Link.submit()
$ie.Quit()