Consuming the SharePoint Online REST API from PowerShell: Part 2

Introduction

A while back ago we already discussed how to  consume SharePoint Online (SPO) REST in PowerShell. Here is a brief recap:

This time I would like demonstrate another approach, in particular  how PowerShell can gain authorization to SharePoint resources by passing an access token to SharePoint with each HTTP request. To issue an access token from Microsoft Azure Access Control Service (ACS) that allows the app access to the resources in the SharePoint tenancy we will implement the corresponding PowerShell function. Let’s get started.

Getting Access Token from Microsoft Azure Access Control Service

The Get-SPOAccessToken function demonstrates how to obtain the access token from a Microsoft Azure Access Control Service (ACS) account that is associated with the customer’s Microsoft Office 365 tenancy:

<#
.Synopsis
Obtain an app-only access token from ACS.
.DESCRIPTION
Retrieves an app-only access token from ACS to call the specified principal
at the specified targetHost. The targetHost must be registered for target principal. If specified realm is
null, the "Realm" setting in web.config will be used instead
.EXAMPLE
Get-SPOAccessToken -Url "https://contoso.sharepoint.com/_api/web&quot; -ClientId "" -ClientSecret ""
#>
Function Get-SPOAccessToken([string]$ClientId,[string]$ClientSecret,[Uri]$WebUri){
$SharePointPrincipal = "00000003-0000-0ff1-ce00-000000000000"
$realm = GetRealmFromTargetUrl TargetApplicationUri $WebUri
$accessToken = GetAppOnlyAccessToken ClientId $ClientId ClientSecret $ClientSecret TargetPrincipalName $SharePointPrincipal TargetHost $WebUri.Authority TargetRealm $realm
return $accessToken.access_token
}
function GetRealmFromTargetUrl([Uri]$TargetApplicationUri)
{
$url = $WebUrl + "/_vti_bin/client.svc"
$headers = @{}
$headers.Add('Authorization','Bearer')
try {
$response = Invoke-WebRequest Uri $TargetApplicationUri Headers $headers Method Get
}
catch [Net.WebException] {
$authResponseHeader = $_.Exception.Response.Headers["WWW-Authenticate"]
#$bearerKey = "Bearer realm="
$bearer = $authResponseHeader.Split(",")[0]
$targetRealm = $bearer.Split("=")[1]
return $targetRealm.Substring(1,$targetRealm.Length2)
}
return $null
}
Function GetAppOnlyAccessToken([string]$ClientId,[string]$ClientSecret,[string]$TargetPrincipalName,[string]$TargetHost,[string]$TargetRealm)
{
$resource = GetFormattedPrincipal PrincipalName $TargetPrincipalName HostName $TargetHost Realm $TargetRealm
$ClientId = GetFormattedPrincipal PrincipalName $ClientId Realm $TargetRealm
$contentType = 'application/x-www-form-urlencoded'
$stsUrl = GetSecurityTokenServiceUrl Realm $TargetRealm
$oauth2Request = CreateAccessTokenRequestWithClientCredentials ClientId $ClientId ClientSecret $ClientSecret Scope $resource
$oauth2Response = Invoke-RestMethod Method Post Uri $stsUrl ContentType $contentType Body $oauth2Request
return $oauth2Response
}
Function GetSecurityTokenServiceUrl([string]$Realm)
{
return "https://accounts.accesscontrol.windows.net/$Realm/tokens/OAuth/2"
}
Function CreateAccessTokenRequestWithClientCredentials([string]$ClientId,[string]$ClientSecret,[string]$Scope)
{
$oauth2Request = @{
'grant_type' = 'client_credentials';
'client_id' = $ClientId;
'client_secret' = $ClientSecret;
'scope' = $Scope;
'resource' = $Scope
}
return $oauth2Request
}
function GetFormattedPrincipal([string]$PrincipalName, [string]$HostName, [string]$Realm)
{
if ($HostName)
{
return "$PrincipalName/$HostName@$Realm"
}
return "$PrincipalName@$Realm"
}

Get-SPOAccessToken function is intended for requesting an access token from Azure ACS, it accepts  Client Id and Client Secret parameters that are generated while App registration with Azure ACS (see “How to register App” for a more details).

Using Invoke-RestMethod in Office 365

Invoke-SPORestMethod function demonstrates how to  include the access token to make a REST API call  to SharePoint, passing the OAuth access token in the HTTP Authorization header:

.\Get-SPOAccessToken.ps1
<#
.Synopsis
Sends an HTTP or HTTPS request to a SharePoint Online REST-compliant web service.
.DESCRIPTION
This function sends an HTTP or HTTPS request to a Representational State
Transfer (REST)-compliant ("RESTful") SharePoint Online web service.
.EXAMPLE
Invoke-SPORestMethod -Uri "https://contoso.sharepoint.com/_api/web&quot; -AccessToken $accessToken
#>
Function Invoke-SPORestMethod()
{
Param(
[Uri]$Uri,
[Object]$Body,
[Hashtable]$Headers,
[Microsoft.PowerShell.Commands.WebRequestMethod]$Method = [Microsoft.PowerShell.Commands.WebRequestMethod]::Get,
[string]$AccessToken
)
$contentType = 'application/json;odata=verbose'
if(-not $Headers) {
$Headers = @{}
}
$Headers["Accept"] = "application/json;odata=verbose"
$Headers.Add('Authorization','Bearer ' + $AccessToken)
Invoke-RestMethod Method $Method Uri $Uri ContentType $contentType Headers $Headers Body $Body
}

Examples

The following example demonstrates how to retrieve List resource properties:

param (
$ClientId,
$ClientSecret,
$WebUri,
$ListTitle
)
.\Get-SPOAccessToken.ps1
Function Get-SPOList([Uri]$WebUri,[string]$ClientId,[string]$ClientSecret,[Uri]$ListTitle)
{
$accessToken = Get-SPOAccessToken ClientId $ClientId ClientSecret $ClientSecret WebUri $WebUri
$endpointUri = "$WebUri/_api/web/lists/getbytitle('$ListTitle')"
$data = Invoke-SPORestMethod Uri $endpointUri AccessToken $accessToken
return $data.d
}
Get-SPOList WebUri $WebUri ClientId $ClientId ClientSecret $ClientSecret ListTitle $ListTitle

view raw
Get-SPOList.ps1
hosted with ❤ by GitHub

But before running the specified script we need to perform one more step in order to grant permissions to the app principal otherwise the unauthorized error will occur as shown on picture below:
Rest401

  • Navigate to http://<SharePointWebsite>/_layouts/15/AppInv.aspx
  • Look up the app based on the Client ID that you just generated and click Lookup, it will find the app principal.  Then paste the AppPermissionRequests XML into the Permissions text box and click CreateAppInv
    Once you click Create, the Trust dialog will appear, click Trust
    AppInv_Trust

That’s it.  Now, after executing the specified script, the output will look like shown below

Get-SPOList-Results

How to register App

Below is provided a step by step instruction how to register an App, for a complete guide follow this article:

  • To create the app identity, navigate to http://<SharePointWebsite>/_layouts/15/AppRegNew.aspx on the tenancy or farm
  • Enter values for the form fields as shown below on picture
    AppNewReg_NewForm
    where
    App ID: App ID, also known as client ID, is a GUID that can be generated (when you click Generate) or pasted into AppRegNew.aspx. The value must be unique for each app, and must be lower case
    App Secret: The app secret, also known as the client secret, is an opaque string. It is generated on the AppRegNew.aspx page by using the Generate button. The following is an example of an app secret: Ywjaoz7DJBGhoLQ2t0IbVCA5pfqqI722ZIVt+ENLk0g=
    Title: Choose your own user-friendly title; for example, PowerShell Console
    App Domain:
    The host name of the remote component of the app for SharePoint
    Redirect URI: The endpoint in your remote application or service to which ACS sends an authentication code
  • Click Create on the form. The page will reload and show a confirmation of the values you entered as shown on picture below
    AppNewReg
  • Save Client Id and Client Secret values. After that you could verify whether Get-SPOAccessToken function returns access token. The picture below shows  the output after executing the command:
    Get-SPOAccessToken -ClientId “1523cf05-b437-4e73-9ad1-a652da8f2ae5” -ClientSecret “Ywjaoz7DJBGhoLQ2t0IbVCA5pfqqI722ZIVt+ENLk0g=” -WebUri “https://contoso.sharepoint.com/&#8221;
    ISE_AccessToken

References

3 thoughts on “Consuming the SharePoint Online REST API from PowerShell: Part 2

  1. Pingback: Office 365( O365 ) – Client application registration, authentication and authorization | For the love of problems :)

  2. Pingback: SharePoint Online にアプリからアクセスする | ブチザッキ

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