SharePoint App-Only Add-ins throwing 401 Unauthorized on newly created O365 tenants

Question

Hi,

we have noticed that our SharePoint AddIn cannot get permissions on a newly created trial O365 tenant.

While getting the ClientContext with ClientID and ClientSecret we get this error "The remote server returned an error: (401) Unauthorized."

We have tried to register a new app-only principal to test if it works on a new tenant by following this documentation from Microsoft:

https://learn.microsoft.com/en-us/sharepoint/dev/solution-guidance/security-apponly-azureacs
After registering and trying again, on the new tenant we got the exact same error "The remote server returned an error: (401) Unauthorized."

But when we tried on an older tenant that we had, it worked fine for both our SharePoint Add-In and for a newly registered principal.

Very simple call using OfficeDevPnP nuget.

OfficeDevPnP.Core.AuthenticationManager am = new OfficeDevPnP.Core.AuthenticationManager();
using (Microsoft.SharePoint.Client.ClientContext context = am.GetAppOnlyAuthenticatedContext(createEntity.AppUrl, clientId, clientSecret))
{
Web web = context.Web;
context.Load(web, w => w.Id, w => w.Title);
context.ExecuteQueryRetry();
}

Is anyone else having the same issue on fresh newly created O365 tenants?

Or maybe there is some new setting to allow using "SharePoint App-Only" authentication?

I have posted the same question to another forum, but was redirected to post here also.
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_sharepoint-mso_win10-mso_o365b/sharepoint-app-only-add-ins-throwing-401/962bfaa2-8604-4e94-ae1c-36ef5b453ed2?tm=1599640808879

Answer 1

I would suggest you to create a service request in admin center,so our engineers could help you check this issue.

---------------------------------
Updated---------------------------
You could try to run below command:

Set-SPOTenant -DisableCustomAppAuthentication $false  

Tip:You need to update the SharePoint Online managed shell to the latest version.

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Answer 2

I am also facing the same issue with new tenant. This is a serious issue with newly created tenant.
The solution is only the command :

 Set-SPOTenant -DisableCustomAppAuthentication $false

Thanks,
Gaurav Goyal

Answer 3

I've been experiencing the same issue since 22/04, however it's on a tenant that has existed for a couple of years.

Answer 4

I was using Azure app service to host my app and facing this issue, Adding following line of code in the startup.Auth.cs in App_start folder fixed my issue

ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12;

Answer 5

Good morning all ,
I need your help
I tried to upload files to a SharePoint online site via an application

Protocol Commands: >>POST https://xxxxxx.sharepoint.com/sites/Transfert_secure/Documents/_api/web/GetFolderByServerRelativeUrl('/sites/Transfert_secure/Documents/Targetfolder')/Files/Add(url='file.txt',overwrite=true) HTTP/1.1

<<HTTP/1.1 401 Unauthorized

I believe that the site should be granted permission through the AD application but I don't know how I could do it ?

Thank you