Handle Conditional Access challenge for Privileged Identity Management on Microsoft Graph

Privileged Identity Management (PIM) for Azure resources api’s are available on Microsoft Graph (MSGraph) so that developers can automate the PIM operations like activation, assignment, etc. To learn more, see http://www.anujchaudhary.com/2018/02/powershell-sample-for-privileged.html

Some organizations enable conditional policies like Multi factor authentication (MFA) for accessing any Azure resources. When users go to PIM through Azure Portal, they are prompted for MFA while logging into the Azure Portal. When they access the PIM UI, everything works since they have already performed MFA.

However, if the users are accessing PIM api’s for Azure resources through MSGraph, they might not be prompted for MFA on login since no conditional access policy might be enabled for MSGraph. When a PIM api is called, it fails with 400 Bad Request invalid_grant error since a conditional access policy is not met for Azure resources.

Example:

HTTP/1.1 400 Bad Request

{

  "error": {

    "code": "invalid_grant",

    "message": "{\"Name\":\"MsalUiRequiredException\",\"Message\":\"AADSTS50076: Due to a configuration change made by your administrator, or because you moved to a new location, you must use multi-factor authentication to access '797f4846-ba00-4fd7-ba43-dac1f8f63013'.\\r\\nTrace ID: 7bdbe148-89e6-4493-a150-93dac7a06c00\\r\\nCorrelation ID: ff221ee5-ebb9-42d0-8f70-dbffde1b2104\\r\\nTimestamp: 2020-09-16 01:16:03Z\",\"Claims\":\"{\\\"access_token\\\":{\\\"capolids\\\":{\\\"essential\\\":true,\\\"values\\\":[\\\"051744ca-6abe-4095-b526-14a7f4033309\\\"]}}}\"}",

    "innerError": {

      "date": "2020-09-16T01:16:03",

      "request-id": "82cd21d1-6413-4512-a2d1-fa1d0a3c5826",

      "client-request-id": "82cd21d1-6413-4512-a2d1-fa1d0a3c5826"

    }

  }

}

To handle this, the user needs to catch the error, get the claims challenge and send in a login request with claims challenge as an extra query string parameter.

To learn more, see https://docs.microsoft.com/en-us/azure/active-directory/develop/conditional-access-dev-guide#scenario-app-performing-the-on-behalf-of-flow

Below is a PowerShell sample which showcases on how to handle the conditional access challenge when calling PIM api's on MSGraph. Just save this as a .ps1 file and run it with PowerShell.

Sceenshot

Source code

#Acquire AAD token

function AcquireToken($claims){

    $clientID = "dabc52c4-106b-4179-9df2-2f791f44ba14"

    $redirectUri = "https://pimmsgraph"

 

    $authority = "https://login.microsoftonline.com/common"

    if($claims -ne $null)

    {

        $authResult = Get-MSALToken -Scopes @("https://graph.microsoft.com/.default") -ClientId $ClientID -RedirectUri $redirectUri -Authority $authority -Interactive -ExtraQueryParameters @{claims=$claims}

        Set-Variable -Name mfaDone -Value $true -Scope Global

    }

    else

    {

        $authResult = Get-MSALToken -Scopes @("https://graph.microsoft.com/.default") -ClientId $ClientID -RedirectUri $redirectUri -Authority $authority -Interactive

    }

    if($authResult -ne $null)

    {

        Write-Host "User logged in successfully ..." -ForegroundColor Green

    }

    Set-Variable -Name headerParams -Value @{'Authorization'="$($authResult.AccessTokenType) $($authResult.AccessToken)"} -Scope Global

    Set-Variable -Name assigneeId -Value $authResult.UserInfo.UniqueId -Scope Global

} 

#List resources

function ListResources(){

    $url = $serviceRoot + "resources?`$filter=(type+eq+'subscription')" 

     Write-Host $url

    $response = Invoke-WebRequest -UseBasicParsing -Headers $headerParams -Uri $url -Method Get

    $resources = ConvertFrom-Json $response.Content

    $i = 0

    $obj = @()

    foreach ($resource in $resources.value)

    {

        $item = New-Object psobject -Property @{

        Id = ++$i

        ResourceId =  $resource.id

        ResourceName =  $resource.displayName

        ResourceType =  $resource.type

    }

    $obj = $obj + $item

}

 

return $obj

}

#Disaplay resources

function DisplayResources(){

    $resources = ListResources

    $resources | Format-Table -AutoSize -Wrap Id,ResourceName,ResourceType

}

 

############################################################################################################################################################################

 

$global:serviceRoot = "https://graph.microsoft.com/beta/privilegedAccess/azureResources/"

$global:MSGraphRoot = "https://graph.microsoft.com/v1.0/"

$global:headerParams = ""

$global:assigneeId = ""

$global:mfaDone = $false;

 

# Install msal.ps

if(!(Get-Module | Where-Object {$_.Name -eq 'PowerShellGet' -and $_.Version -ge '2.2.4.1'})) { Install-Module PowerShellGet -Force }

if(!(Get-Package msal.ps)) { Install-Package msal.ps }

$Authed = AcquireToken $global:clientID $global:redirectUri $global:resourceAppIdURI $global:authority $false

if ($Authed -eq $false)

{

    return

}

try

{

    DisplayResources

}

catch

{

    $stream = $_.Exception.Response.GetResponseStream()

    $stream.Position = 0;

    $streamReader = New-Object System.IO.StreamReader($stream)

    $err = $streamReader.ReadToEnd()

    $streamReader.Close()

    $stream.Close()

 

    if($err.Contains("invalid_grant"))

    {

        $errorObject = ConvertFrom-Json $err

        $message = ConvertFrom-Json $errorObject.error.message

        $claims = $message.claims

        Write-Host "Prompting the user again since since a conditional access policy is enabled..." -ForegroundColor Green

        AcquireToken $claims

        DisplayResources

    }

    else

    {

        Write-Host $err -ForegroundColor Red

    }

}

 

Write-Host ""