How to get/add/changed allowed server variables of IIS Web Site with PowerShell?

Question

I'm trying to make a PS script that creates an IIS web page, configures a reverse proxy via URL Rewrite and I'm stuck on how to add allowed server variables via PowerShell.

Does anyone know how to add these variables via powershell for the IIS website?

Answer 1

FYI adding server variable on server level by powershell:

Add-WebConfiguration /system.webServer/rewrite/allowedServerVariables -atIndex 0 -value @{name="RESPONSE_SERVER"}

this will add the following configuration in applicationhost.config

<system.webServer>
...
    <rewrite>
    ...
        <allowedServerVariables>
            <add name="RESPONSE_SERVER" />
        </allowedServerVariables>
    ...
    </rewrite>
</system.webServer>

Answer 2

Updated 2024/09/24

this answer works with PowerShell 7+

1. import the iis module

Import-Module IISAdministration

2. create the following two functions:

function Enable-IisServerVariable($variable) {
    $section = Get-IISConfigSection -SectionPath "system.webServer/rewrite/allowedServerVariables"
    $collection = Get-IISConfigCollection -ConfigElement $section
    $existingVariables = $collection | ForEach-Object { $_.Attributes["name"].Value }

    if (-not ($existingVariables -contains $variable)) {
        New-IISConfigCollectionElement -ConfigCollection $collection -ConfigAttribute @{"Name" = $variable}
        Write-Host "Server variable '$variable' has been added."
    } else {
        Write-Host "Server variable '$variable' is already enabled."
    }
}

function Enable-ReverseProxyHeaderForwarding() {
    foreach ($variable in @("HTTP_X_FORWARDED_PROTO", "HTTP_X_FORWARDED_HOST", "HTTP_X_FORWARDED_FOR")) {
        Enable-IisServerVariable $variable
    }
}

3. execute the function:

Enable-ReverseProxyHeaderForwarding

Original Answer

as noted in @matija's answer, you will need to ensure you have the web admin module loaded:

Import-Module WebAdministration

then, building on @lia's answer, you can define a function to add multiple variables in an idempotent fashion like this:

function Enable-ReverseProxyHeaderForwarding() {
    $requiredVariables = @("HTTP_X_FORWARDED_PROTO", "HTTP_X_FORWARDED_HOST", "HTTP_X_FORWARDED_FOR")
    $existingVariables = Get-WebConfiguration -Filter "/system.webServer/rewrite/allowedServerVariables/add" -PSPath "IIS:\Sites\" | ForEach-Object { $_.name }

    foreach ($variable in $requiredVariables) {
        if (-not ($existingVariables -contains $variable)) {
            Add-WebConfiguration "/system.webServer/rewrite/allowedServerVariables" -value @{name = $variable }
        }
    }
}

and then execute the function:

Enable-ReverseProxyHeaderForwarding