$url = "https://TestSite.sharepoint.com"
$username = "Testuser@testsite.sharepoint.com"
$password = "Lidf$ijsd@f$"
$appfilepath = "C:tempapp.app"
$Password = $password |ConvertTo-SecureString -AsPlainText -force
try
{
    Write-Host "Load CSOM DLLs" -foregroundcolor black -backgroundcolor yellow Set-Location
    $loadInfo1 = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client")
    $loadInfo2 = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.Runtime")
    Write-Host "CSOM DLLs loaded succeefully" -foregroundcolor black -backgroundcolor Green
}
catch
{
    Write-Host "Problem in loading CSOM DLLs : $_.Exception.Message" -foregroundcolor black -backgroundcolor Red
    return
}
try
{
    Write-Host "Authenticate tenant site $url and get ClientContext object" -foregroundcolor black -backgroundcolor yellow
    $context = New-Object Microsoft.SharePoint.Client.ClientContext($url)
    $credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $password)
    $context.Credentials = $credentials
    $web = $context.Web
    $site = $context.Site
    $context.Load($web)
    $context.Load($site)
    $context.ExecuteQuery()
    Write-Host "Authentication to online site $url and get ClientContext DLLS succeeful" -foregroundcolor black -backgroundcolor Green
}
catch
{
    Write-Host "Unable to authenticate to online site. Error : $_.Exception.Message" -foregroundcolor black -backgroundcolor Red
    return
}
try
{
    $appIoStream = New-Object IO.FileStream($appfilepath,[System.IO.FileMode]::Open)
    $appInstance = $web.LoadAndInstallApp($appIoStream) | Out-Null
    $context.ExecuteQuery()
    Write-Host $appInstance.Id
}
catch
{
    Write-Host "Unable to Install App Error : $_.Exception.Message" -foregroundcolor black -backgroundcolor Red
    return
}