Tag Archives: ACS

Azure Access Control

Providing ACS permissions for app to access SharePoint

Microsoft retires ACS

Let me quote Microsoft just to start (Dec 18, 2023):

  • “SharePoint App-Only is the older, but still very relevant, model of setting up app-principals.”
  • “… we will be retiring the use of Azure ACS (Access Control Services) for SharePoint Online auth needs and believe Microsoft 365 customers will be better served by modern auth…”
  • “Azure ACS will stop working for new tenants as of November 1st, 2024 and it will stop working for existing tenants and will be fully retired as of April 2nd, 2026…
    There will not be an option to extend using Azure ACS with SharePoint Online beyond April 2nd, 2026″
  • “… we recommend switching those applications to use Microsoft Entra ID for authorization and authentication needs…”

So, for new development it is strictly recommended to use Azure Registered Apps to access Microsoft 365 resources programmatically.

You still need ACS in some cases

But, as always, it all is not so simple, as

  • there are still plenty of 3-rd party applications written and used widely that require ACS-based permissions. Moreover, there are still some 1-st party applications (Microsoft apps and services) that require ACS-based permissions
  • though Microsoft Graph API is good and provide a lot of functionality and is developing rapidly, it cannot cover all SharePoint dev’s needs, so using SharePoint REST API could be unavoidable… and that is where some complications are coming
  • permissions to specific SharePoint sites (not to all tenant sites, but to one or several SharePoint sites in tenant) for apps is done via Sites.Selected, but this works to entire site collection only. E.g. via Sites.Selected you cannot provide granular permissions (e.g. to specific list) for an app, which might be crucial in some cases, so you’d still have to use ACS-based permissions

Hopefully, Microsoft will resolve all the issues above before April 2026… But for now we have to live with both – Azure Registered applications and API permissions configured in Entra ID and with SharePoint app-only service principals and ACS-based permissions.

Azure Apps and Entra Id vs SharePoint app-only spn and ACS

Comparison between Azure Apps and Entra Id API permissions vs SharePoint app-only spn and ACS-based permissions

ACS-based SharePoint app/permissionsApps registered in Azure with Sites.Selected API permissions
support authentication with client secret only, secret is valid for 1 year exactlysupport authentication with client secret and/or certificate, custom expiration time
support granular access to SharePoint site content – e.g. to entire site collection or web (subsite) or a specific listsupport only access to entire site collection (but Microsoft is working on granular access)
support only classic SharePoint REST API and CSOMsupport both – classic SharePoint REST API and CSOM and Microsoft Graph API
app id (client id) is created via appregnew.aspx at a specific SharePoint site by site collection administratorapp id (client id) is created in Azure portal, API Sites.Selected permissions are configured via Azure portal and require tenant admin consent
permissions for the app to a site are provided at the site by site collection administrator via appinv.aspx pagepermissions for the App to to a specific SharePoint site are provided by SharePoint admin with PowerShell script or Graph API calls
logging audit log

SharePoint app-only service principal and ACS-based permissions

Since SharePoint app-only service principals and ACS-based permissions were introduced for SharePoint 2013 as part of Add-Ins feature – there are plenty of articles from Microsoft and MVPs and SharePoint gurus on this. But I would like to highlight one thing:

  • AppRegNew page creates service principal and allows authentication
  • AppInv page provides permissions and allows authorization to SharePoint

Check SharePoint AppRegNew.aspx and AppInv.aspx for details

Recommended transition tactics

WIP…

References

SharePoint Add-Ins and ASC retirement

Microsoft announced retirement for SharePoint Add-Ins and ASC-based app permissions (SharePoint app-only principals). Let me summarize here:

  • SharePoint Add-Ins, ASC-based app permissions and SharePoint app-only principals
  • Timeline of retirement and future plans
  • How to detect if there are legacy service principals used in the environment
  • Migration guidance

Timeline

Known key retirement milestone dates:

  • Mar 2024 – Microsoft will stop accepting new Add-In submission to app store
  • Jul 2024 – Microsoft will stop ability for customers to acquire add-ins from App Store (*)
  • using ACS and Add-ins will be blocked for new tenants since Nov 2024
  • using ACS and Add-ins will be blocked for all tenants since Apr 2026

(*) SPFx based solutions will continue to be available

So timeline is generous, and we have plenty of time to

Detect if there are any legacy service principals used in the environment

WIP…

Sites.Selected permissions provisioning automation

Scenario

You administer Microsoft 365 SharePoint Online. Part of your daily activities is providing Microsoft Graph and SharePoint Sites.Selected API permissions to other users (developers).

In Aug/Sep 2023 Microsoft pushed an update that prevents site collection admins to create or update an Azure Access Control (ACS) principal (that was the way most of developers used to get Client Id and Client secret to access SharePoint site). So your users are probably getting something like Your SharePoint tenant admin doesn’t allow site collection admins to create or update an Azure Access Control (ACS) principal message attempting to create or update SharePoint App-only principal at AppRegNew.aspx or AppInv.aspx pages. Here are more details on the issue.

Microsoft and MVPs shared some technique how to provide Sites.Selected API permissions, but dealing with scripts manually, elevating individual permissions every time you need to run the script – it all takes time and not very efficient. More and more devs are reaching you on the app. So you want to automate this process.

Solution

Solution architecture

My way to automate it includes:

  • SharePoint list as a frontend
    here you can accept intake requests, organize approval workflow and display automation results
  • Azure Function App as a backend
    here will be your PowerShell script hosted that runs on scheduled basis and takes care of actual permissions provisioning

Solution details

High-level, getting application permissions to some specific SharePoint site is a two-step process:

  1. get application registration in Azure and properly configure it
  2. get permissions for this application to a specific SharePoint site

For the first step – check this and this articles. I’ll focus on the second step below.

You can provide Sites.Selected permissions for the app to a site with

I will be using second one one. Also PnP.PowerShell will be used to get access to SharePoint intake site and read/update requests from SharePoint list and so on.

Azure App Registration

I registered an admin Application in Azure – “SharePoint Automation App”, added Graph Sites.FullControl.All and SharePoint Sites.FullControl.All permissions, then added Microsoft Graph Directory.Read.All permissions and got tenant admin consent:

I generated a self-signed certificate and added it to the app:

This app will be used to call provide permissions, and to connect to the SharePoint front-end.

Users will register their applications in Azure, add Graph Sites.Selected and SharePoint Sites.Selected permissions, got tenant admin consent, then request permissions to the specific site by creating an intake request – new list item.

Front-End SharePoint Site

I created a SharePoint site for automation. This site will play a front-end role for users. I created a list “Sites.Selected” and updated list columns so I have the following fields:

  • Target Site Url
  • Application Id
  • Permissions (read/write)
  • Automation Output

In real-world (Prod) – You can (should) also implement approval workflow as you’d provide permissions for the application to the site only with this site owner approval. The PowerShell code behind should also validate site owner’s consent with app access to site. But for the sake of simplicity I’ll skip this in my demo.

Azure Function App

I created an Azure Function App with the following parameters:
– Runtime stack: PowerShell Core
– Version: 7.2.
– OS: Windows
– Hosting plan: Consumption

And then PowerShell timer-triggered function in Visual Studio Code.

Function requirements.psd1 (it takes a few hours for Azure to install modules; while modules are installing – you might see “[Warning] The first managed dependency download is in progress, function execution will continue when it’s done. Depending on the content of requirements.psd1, this can take a few minutes. Subsequent function executions will not block and updates will be performed in the background.”):

@{
    'Az' = '10.*'
    'PnP.PowerShell' = '2.*'
}

Azure Az module to access other Azure resources. PnP.PowerShell module will be used to access SharePoint.

I will keep my admin Azure registered app in a key vault, so need somehow to let the key vault know that this specific app can access this specific credentials. So I enabled system assigned managed Identity for the Function App:

MS: “This resource is registered with Azure Active Directory. The managed identity can be configured to allow access to other resources…”.
I’m going to use an object (principal) Id of this function to grant access to keyvault.

Azure key vault

Surely we do not hard-code app secrets. So we need a key vault o store app credentials.

I created a key vault under the same resource group in Azure and named it “SharePointAutomationDemo”. Then I added a roles assignment – “Key Vault Secret User” and “Key vault Reader” to the Function App via it’s managed identity:

I also assigned “Key Vault Administrator” role to the user (developer) who will add certificates/secrets to this key vault and develop Azure function code.

Code repository

https://github.com/VladilenK/Sites.Selected-Automation

Videos

Part 1: Getting Azure App Registration with Sites.Selected API Permissions

Part 2: SharePoint and Microsoft Graph API Sites.Selected permissions provisioning automation

Your SharePoint tenant admin doesn’t allow site collection admins…

Scenario

You are trying to register an application at SharePoint site with appregnew.aspx page and you are getting an error or notification message “Your SharePoint tenant admin doesn’t allow site collection admins to create an Azure Access Control (ACS) principal“.

Your SharePoint tenant admin doesn't allow site collection admins to create an Azure Access Control (ACS) principal. Please contact your SharePoint tenant administrator

Or you are trying to provide ACS-based permissions for an application to SharePoint site with appinv.aspx page and you are getting “Your SharePoint tenant admin doesn’t allow site collection admins to update app permissions. Please contact your SharePoint administrator.

Your SharePoint tenant admin doesn't allow site collection admins to update app permissions. Please contact your SharePoint tenant administrator

You can still view and even delete your apps permissions from /_layouts/15/appprincipals.aspx page:

Reason

This is due to a recent update to Microsoft 365 (tenant governance security measures enhancement MC660075) implemented by Microsoft in Aug/Sep 2023. According to the update, only tenant administrators can create or update ACS service principal by default.

The root cause for this is that the Microsoft is pushing developers out of that legacy ACS-based SharePoint Apps-only service principals towards Azure-registered applications with Sites.Selected API permissions as they are more secure etc.
In Nov 2023 Microsoft announcement retirement of ACS principals.

Key differences between ASC and Sites.Selected are:

ACS-based SharePoint app/permissionsApps registered in Azure with Sites.Selected API permissions
Support authentication with client secret only, Secrets are valid for 1 year exactly.Support authentication with client secret and/or certificate, custom expiration time.
Support granular access to SharePoint site, e.g. to site collection or web (subsite) or a specific list or library.Support only access to entire site collection (but Microsoft says granular access is coming)
Support only classic SharePoint REST API and CSOMSupport both – classic SharePoint REST API and CSOM and Microsoft Graph API
App id (client id) is created via appregnew.aspx at a specific SharePoint site by site collection administrator (disabled in Sep 2023).App id (client id) is created in Azure portal (Entra Id), API Sites.Selected permissions are configured via Azure portal (Entra Id) and require tenant admin consent.
Permissions for the app to a site are provided at the site by site collection administrator via appinv.aspx page (disabled in Sep 2023).Permissions for the App to to a specific SharePoint site are provided via Graph API by SharePoint admin with PowerShell script.

Solution #1 – switch to Sites.Selected

  1. Register an application in Azure (via Entra Id – Azure portal GUI, PowerShell script or your company’s specific helpdesk/servicedesk request)
  2. Update the app so both – MS Graph API Sites.Selected and SharePoint Sites.Selected permissions are configured, then
  3. API permissions must be consented – so you’d seek/request your tenant admin consent
  4. Obtain and upload client certificate (recommended) or generate client secret
    (at this moment you should be able to authenticate to tenant)
  5. Request access for the app to a specific SharePoint site – your SharePoint service admin should be able to do that
    (at this moment you should be able to authorize to your SharePoint site).
  6. Validate your app has access to the target SharePoint site with PowerShell
    (check validation scripts below under References).
  7. Use recommended by Microsoft technique, code samples are available for the most popular languages/platforms – Python, C#, Java etc. (check below under References).
  8. Secure your certificate and/or secret. It is not a good idea to use hard-coded secrets, so consider using special services/storages for secrets (aka Vaults)

If you are hosting your application in Azure – consider using managed identity.

Step-by-step guide with screenshot – how to get app with Sites.Selected permissions

Video guide on using Sites.Selected to access SharePoint as application:

There are 3-rd party (and Microsoft) apps developed using classic approach (examples – Azure data Factory, Alteryx). So in some cases Sites.Selected permissions are not enough to get access to SharePoint.

Solution #2 – admin to register/update an ACS app

This option is acceptable if you have existing application that require ACS-based access.
This option is not recommended for new development, as ACS is deprecated and scheduled for retirement.

Microsoft (MC660075 in Message Center): “site collection admin will be unable to register app or update app permissions through above pages unless authorized explicitly by the SharePoint tenant admin” and “With this update site owners will not be able to register/update apps unless the tenant admin explicitly allows it.”

That is incorrect. Site collection admin cannot register app (appregnew) or provide permissions to the app (appinv) anymore. Tenant admin does not authorize site collection admins. Instead tenant (or SharePoint) admin can register an app or provide permissions to the app at a specific site (not changing the entire default behavior back…). But there was no such option (!) in the middle of October 2023, when this feature was enabled at all tenants. Even having a SharePoint admin or tenant admin permissions – if you tried to register an app with AppRegNew.aspx – you got the same error message “Your SharePoint tenant admin doesn’t allow site collection admins to…”.

Later (Checked today – Nov 6, 2023) it seems like Microsoft has implemented it! E.g. now SharePoint or tenant admin is able to register an app with AppRegNew.aspx or update it with AppInv.aspx at any specific site collection. SharePoint or tenant admin must also be among this site collection admins.

It is ok (and I’d say the preferred way) to provide ACS permissions to the app registered in Azure, so do not register apps in SharePoint anymore (do not use AppRegNew.aspx).

Bottom line: if ACS-based permissions are required for app here you go:

  • register application in Azure (Entra id)
  • activate your SharePoint service/tenant admin role
  • ensure you are also target site collection administrator
  • navigate to the site appinv.aspx page – e.g.
    “https://yourtenant.sharepoint.com/sites/yoursite/_layouts/15/appinv.aspx”
    and us Azure registered app (client) Id. E.g. for lookup provide
    • Azure registered app (client) Id for – click lookup
    • localhost as app domain
    • https://localhost as redirect url
    • Permission Request XML – depending on permissions you need, e.g. for full app access to entire site collection:
<AppPermissionRequests AllowAppOnlyPolicy="true">  
   <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" 
    Right="FullControl" />
</AppPermissionRequests>

Solution #3 – step back (not recommended)

It is possible to switch back this new default behavior that prevents site collection admin to register/update apps at SharePoint. This is done with PowerShell command

Set-SPOTenant -SiteOwnerManageLegacyServicePrincipalEnabled $true

To run this command – you’d need to be a SharePoint service or tenant admin.

But this will be a step back on your journey in improving m365 tenant safety, as after that you’ll have a self-registered service principals out of control again. So devs will be using it not being aware of ACS retirement and when Microsoft switch off ACS – it will be a disaster, as all app will stop working. That is why Microsoft implemented this feature to soft-disable ACS and allowed us 2 years to redesign or apps and migrate from ACS to Entra Id apps with Sites.Selected. So this solution is not recommended.

In case you really need an exception to provide an ACS-based service principal – there is Solution number 2.

Full text of Microsoft’s MC660075 message

(Updated) SharePoint admin control for App registration / update

Tag
MAJOR UPDATE ADMIN IMPACT FEATURE UPDATE

Message Summary
Updated August 30, 2023: We have updated the content below for clarity. Thank you for your patience.

This is an enhancement to the security measures for administrative governance that modifies the default procedures for SharePoint app registration via AppRegNew.aspx page and permission updates via AppInv.aspx page. Following the implementation of this change, site collection admin will be unable to register app or update app permissions through above pages unless authorized explicitly by the SharePoint tenant admin.

Upon attempting to register an application on AppRegnew.aspx page, a notification will be displayed stating “Your SharePoint tenant admin doesn’t allow site collection admins to create an Azure Access Control (ACS) principal. Please contact your SharePoint tenant administrator.”

Similarly, upon attempting to update app permissions on AppInv.aspx page, a notification will be displayed stating “Your SharePoint tenant admin doesn’t allow site collection admins to update app permissions. Please contact your SharePoint tenant administrator.”

Kindly note that app registration and permission update via Microsoft Azure portal are not impacted by this change.

When this will happen:

The rollout process is scheduled to commence in late August and is expected to conclude in mid-September.

How this will affect your organization:

With this update site owners will not be able to register/update apps unless the tenant admin explicitly allows it.

To modify the default behavior, the tenant administrator must execute the following shell command to explicitly establish the flag as TRUE, thereby superseding the default value of FALSE. The service principal can only be created or updated by the tenant administrator by default. However, when the flag is set to TRUE, both the SharePoint tenant admin and site collection admin will be able to create or update the service principal through SharePoint.

The shell command is: Set-SPOTenant -SiteOwnerManageLegacyServicePrincipalEnabled $true

Note: The property ‘SiteOwnerManageLegacyServicePrincipalEnabled’ becomes visible in tenant settings after SharePoint Online Management shell is updated to 16.0.23710.12000 or a later version. But before this rollout, the value will always be TRUE even explicitly set to FALSE. It will only automatically be switched to FALSE as the default value after the rollout is launched.

What you need to do to prepare:

No proactive measures are required to prepare for this change. Nevertheless, it is advisable to inform your users of this modification and update any relevant documentation as necessary.

References

Sites.Selected API permissions for SharePoint access

Sites.Selected permissions are required for the non-interactive application to get access to a specific SharePoint site using Microsoft Graph API and/or SharePoint API.

Below are the steps to get access to SharePoint site with Sites.Selected API permissions:

1. Register an application in Azure (via Azure portal GUI, PowerShell script or helpdesk/servicedesk request), e.g. with GUI you’d login to portal.azure.com,
the search for “App registrations” and select “+ New registration”:

2. Update the app “API permissions” – so both – MS Graph API Sites.Selected and SharePoint Sites.Selected application API permissions are configured:

Provide or request tenant admin consent for your API permissions. Finally your app registration “API permissions” should look like:

3. Under Certificates and secrets – generate client secret, copy secret value to safe location.

4. At the Overview page – grab your app client id and tenant id :

At this moment, having tenant id, app (client) id and client secret – you should be able to authenticate against Microsoft 365 tenant with app-only authentication path.

But! Having just Sites.Selected API permissions configured for app does not mean your app has access to SharePoint site. Access for the app to a specific site is provided by SharePoint team using PowerShell script or Graph API calls. That leads us to the next step.

5. Request access for the app to the SharePoint site (your SharePoint service admin should be able to do that via PowerShell script or Graph API calls )
Here is the Graph API

6. Once your SharePoint tenant/service admin confirmed that access has been provided – you can use app client id and client secret to work with SharePoint from your code using Graph API.
If any concerns – you can validate your app access to the target SharePoint site with simple PowerShell scripts: here is the sample code

7. Secure your certificate and/or secret
You do not hard-code secrets. Consider using vault to keep certificate/secret. If you host your application in Azure – consider using managed identity.

Note 1: Sites.Selected API permissions allows you call Microsoft Graph API with client Id and client secret. Calling SharePoint API with client secret is not supported. You have to use client id and certificate to call SharePoint API having app with Sites.Selected permissions.

Call SharePoint API with client Id and client secret is possible only if ACS-based permissions are provided for the app to the site, which is not recommended (see below).

Comparison between Azure Apps and Entra Id Sites.Selected API permissions vs SharePoint app-only spn and ACS-based permissions.

Note 2: ACS-based permissions are going to be deprecated soon:
Your SharePoint admin doesn’t allow site owners to create/update ACS principal ⋆ Vladilen Microsoft 365 engineer

Update:
Microsoft announced decommissioning of ACS permissions. So do not use ACS for any new development.

It might be acceptable to provide ACS permissions for existing custom apps or 3-rd party or Microsoft apps/web apps (e.g. Alteryx, Azure Data factory) – apps that only support client id and secret and using SharePoint API under the hood – but just to not to break business processes and being aware of ACS EOL and planning a replacement of theses apps before 2026.

References

SharePoint AppRegNew.aspx and AppInv.aspx

There are well-known SharePoint app-only service principals and ACS-based permissions. It is kind of old-school way – introduced as part of Add-Ins for SharePoint 2013 – to get unattended access to SharePoint site (application access, i.e. access without user presence). Such apps are called daemon apps or service apps or background jobs etc…

Microsoft announced retirement of ACS in 2026 and takes measures to stop using ACS in new and existing tenants. For you to smoothly switch to new, recommended Entra Id based service principals and permissions – it is important to know some details about classic app-only service principals and ACS-based permissions.

As you know, any access is a two-step procedure:

  • Authentication, when systems ensures you are indeed the one you claim you are
  • Authorization, when system grants you access to the resource, as it knows that this id is allowed to access such and such resource with these permissions

So, when it comes to deprecated SharePoint app-only service principals and ACS-based permissions, AppRegNew is responsible for authentication and AppInv is responsible for authorization.

AppRegNew.aspx

To get a SharePoint app-only service principal – you’d need to register a new one at any SharePoint site using the AppRegNew.aspx page. This page is not available from GUI, so you’d need to type the Url manually. You’d need to be a site collection admin to register a new app.

Let say, your site Url is “https://YourTenant.sharepoint.com/teams/YourSite“.
Then this appregnew page’s Url would be
“https://YourTenant.sharepoint.com/teams/YourSite/_layouts/15/appregnew.aspx

If you go to this page, you’ll see (*) something like

You’d click generate client id, then generate client secret and type your app display name. I usually use “localhost” as app domain and “https://localhost” as redirect Url.

If all good – you’d get app id (client id) and app secret (client secret) and you’d be able to authenticate to your SharePoint site.

AppInv.aspx

Providing permissions for your SharePoint app-only service principal to your SharePoint site is done using AppInv.aspx page. This page is also not available from GUI, so you’d need to type the Url manually again. You’d need to be a site collection admin to use this page.

Let say, your site Url is “https://YourTenant.sharepoint.com/teams/YourSite“.
Then this appinv page’s Url would be
“https://YourTenant.sharepoint.com/teams/YourSite/_layouts/15/appinv.aspx

If you go to this page, you’ll see (*) something like

At this moment – you need to enter app (client) id here and click lookup – so all the app metadata would be populated, then you’d need to enter Permission Request XML.
Via this “Permission Request XML” you are specifying exact permissions your app will have in this site. E.g. you can specify scope – all site collection or one specific subsite (web) or even one specific list or library. Also you can specify permissions level – e.g. read, read/write, manage or full control. This is tricky, but let me share some examples with you.

Permission Request XML for the app to have full control over entire site collection:

<AppPermissionRequests AllowAppOnlyPolicy="true">  
   <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" 
    Right="FullControl" />
</AppPermissionRequests>

Permission Request XML for the app to have read access to a subsite (web):

<AppPermissionRequests AllowAppOnlyPolicy="true">  
  <AppPermissionRequest Scope="http://sharepoint/content/sitecollection/web" 
   Right="Read" />
</AppPermissionRequests>

Permission Request XML for the app to have read/write access to a list/library:

<AppPermissionRequests AllowAppOnlyPolicy="true">  
   <AppPermissionRequest Scope="http://sharepoint/content/sitecollection/web/list" 
    Right="Write" />
</AppPermissionRequests>

Any mistake in XML might prevent app access, so be very careful.

Finally, your AppInv.aspx page would look like

If you specify scope as web – you’d do it on the specific web url, e.g.
“https://YourTenant.sharepoint.com/teams/YourSite/SubSite/_layouts/15/appinv.aspx”

If you specify scope as list – you’d do it on the specific web url, e.g.
“https://YourTenant.sharepoint.com/teams/YourSite/SubSite/_layouts/15/appinv.aspx”
and after you click “Save” – there will be a page – you’ll be asked to choose a list from available web lists.

After all, you’ll be asked to confirm that you trust the app:

And after that your app (SharePoint app-only service principal) will have access (ACS-based access) to you site.

AppPrincipals.aspx

From site settings page (/_layouts/15/settings.aspx) you should be able to see apps registered on your site with “Site app permissions” or “Site collection app permissions” links available via GUI. That would be “appprincipals.aspx” page.

Unfortunately, you cannot see you app permissions here or your secret expiration time. Some date can be pulled via PowerShell with Get-PnPAzureACSPrincipal

Possible complications

After Microsoft announced retirement of ACS – you can see this message on appinv and appregnew pages:

You might also see “Your SharePoint tenant admin doesn’t allow site collection admins to create an Azure Access Control (ACS) principal” message at appregnew page and “Your SharePoint tenant admin doesn’t allow site collection admins to update app permissions. Please contact your SharePoint administrator.” at appinv page.

That’s because a recent update to Microsoft 365 (MC660075) pushed by Microsoft in Aug/Sep 2023 changes default behavior so only tenant administrators can create or update ACS service principal by default.

If you are facing issues above – or you want to switch to modern Entra Id service principals, but by some reasons you need ACS-based permissions – here is the article on “Entra Id vs ACS for SharePoint and how to survive during transition period

References