How to do ACS setup for SharePoint app only authentication for SharePoint server (On-Premise)?

This process works for online but does not work for on prem versions

Hi @Yichen Name ,

SharePoint App-Only is the older, but still very relevant, model of setting up app-principals. This model works for both SharePoint Online and SharePoint 2013/2016/2019 on-premises and is ideal to prepare your applications for migration from SharePoint on-premises to SharePoint Online. Below steps show how to setup an app principal with tenant full control permissions, but obviously you could also grant just read permissions using this approach.

Navigate to a site in your tenant (e.g. https://contoso.sharepoint.com) and then call the appregnew.aspx page (e.g. https://contoso.sharepoint.com/_layouts/15/appregnew.aspx). In this page click on the Generate button to generate a client id and client secret and fill the remaining information like shown in the screen-shot below.

Next step is granting permissions to the newly created principal. Since we're granting tenant scoped permissions this granting can only be done via the appinv.aspx page on the tenant administration site. You can reach this site via https://contoso-admin.sharepoint.com/_layouts/15/appinv.aspx. Once the page is loaded add your client id and look up the created principal:

To grant permissions, you'll need to provide the permission XML that describes the needed permissions. Since this application needs to be able to access all sites + also uses search with app-only it needs below permissions:

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

When you click on Create you'll be presented with a permission consent dialog. Press Trust It to grant the permissions.

If you want to utilize the generated app-only registration with PnP PowerShell, you can do so by connecting to your SharePoint On-Premises or Online environment using:

Connect-PnPOnline -Url https://contoso.sharepoint.com/sites/demo -ClientId [Your Client ID] -ClientSecret "[Your Client Secret]"

For more information, please refer to:

https://learn.microsoft.com/en-us/sharepoint/dev/solution-guidance/security-apponly

https://www.wictorwilen.se/blog/sharepoint-2013-using-the-app-only-policy-and-app-principals-instead-of-username-and-password-combos/

https://learn.microsoft.com/en-us/sharepoint/security-for-sharepoint-server/plan-for-app-authentication-in-sharepoint-server

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