Update-WebAppSettingsFromJson.ps1

function Update-AppSettings($resourceGroup, $site, $slot, $inputFile)
{
    $webApp = Get-AzureRMWebAppSlot -ResourceGroupName $resourceGroup -Name $site -Slot $slot

    $appSettingList = $webApp.SiteConfig.AppSettings

    $hash = @{}
    ForEach ($kvp in $appSettingList) {
        $hash[$kvp.Name] = $kvp.Value
    }
    
    $json = Get-Content -Raw -Path inputFile | ConvertFrom-Json

    foreach ($item in ($json.PSObject.Members | ?{ $_.MemberType -eq 'NoteProperty'})) {
        $hash[$item.Name] = $item.Value
    }
   
    Set-AzureRMWebAppSlot -ResourceGroupName $resourceGroup -Name $site -AppSettings $hash -Slot $slot
}