SharePointOnline CSOM 401 Unauthorized Using Provided Access Token

Question

I am building a feature that automates the retrieval of documents and other SharePoint files from a Web API, but I'm having a difficult time getting authorized to perform even basic read operations. I am testing this in a .NET 6 console application using the Microsoft.SharePointOnline.CSOM NuGet package.

I have registered an application in Azure Active Directory and given it the Sites.Read.All permission. I've taken the ClientID, ClientSecret and TenantID as reported by that registered application and I'm using those in my console application. I can retrieve an access token without issue, and decoding that JWT shows that it comes with Sites.Read.All permission. But regardless of what I try, ClientContext.ExecuteQueryAsync() consistently throws an exception complaining that the remote server responded with a 401.

Here is the code that I'm testing this with:

var clientId = "myClientId";
var clientSecret = "myClientSecret";
var tenantId = "myTenantId";
var authority = "https://login.microsoftonline.com/" + tenantId;
var siteUrl = "https://myorg.sharepoint.com";

var app = new ConfidentialClientApplicationBuilder
    .Create()
    .WithClientSecret(clientSecret)
    .WithAuthority(authority)
    .WithTenantId(tenantId)
    .Build();

var paramBuilder = app.AcquireTokenForClient(new[] { siteUrl + "/.default" });
var authResult = await paramBuilder.ExecuteAsync();

// authResult has successfully retrieved an access token at this point

var context = new ClientContext(siteUrl);
context.ExecutingWebRequest += (_, e) =>
{
    e.WebRequestExecutor.RequestHeaders["Authorization"] = "Bearer " + authResult.AccessToken;
}

context.Load(context.Web);

await context.ExecuteQueryAsync(); // 401 is thrown here

var title = context.Web.Title;

I have tried several different ways of getting around this to no avail:

• I have gone to the Admin center of my SharePoint site and given the app FullControl permissions, as well as giving the app those permissions in Azure AD. This doesn't seem to have changed anything, I still get the same 401.
• I have registered an entirely new app directly from my SharePoint sub-site admin center and given it FullControl permissions. I used the new client ID and client secret that were generated, and I was able to get back an access token. No luck, still get the 401 calling ClientContext.ExecuteQueryAsync()
• I have tried changing my siteUrl to a SharePoint site-specific URL (e.g. https://myorg.sharepoint.com/sites/mySite), but once I do that I am no longer able to retrieve an access token. I instead get an Msal exception thrown, AADSTS500011, which reads:

"The resource principal named https://myorg.sharepoint.com/sites/mysite was not found in the tenant named (my tenant). This can happen if the application has not been installed by the administrator of the tenant or consented to by any user in the tenant. You might have sent your authentication request to the wrong tenant.

• I have also tried using the base siteUrl to retrieve the token, then giving the site-specific URL to ClientContext. I get the same 401 result.
• I have tried several different authorities in case the token I'm being provided is invalid. I've tried using the V1 token URL, the V2 token URL, no token-specific URL (only the default authority address + tenant ID). All of these return an access token, but none of them avoid the 401.
• A MS documentation article suggests appending an additional "/" to the requested .default scope in instances where a 401 is being returned (e.g. https://myorg.sharepoint.com/sites/mysite//.default). This doesn't seem to have changed anything.

My application seems to have the permissions it needs to do this basic read operation, but I am continually rebuffed. I am using the ClientID, ClientSecret and Tenant ID as copied directly from the AAD application page. The code I'm using above is recommended by Microsoft to use the new SharePointOnline.CSOM package. What am I missing here?

Answer 1

I wound up "solving" this problem by using the PnP.Framework NuGet package instead of Microsoft.SharePointOnline.CSOM. I changed nothing else about my app registration or its designated permissions, and PnP.Framework was able to handle it without issue (and with fewer arguments). It seems to know something that SharePointOnline.CSOM doesn't considering that the following simple console app works:

using System;
using PnP.Framework

const string clientId = "myClientId";
const string clientSecret = "myClientSecret";
const string siteUrl = "https://myorg.sharepoint.com/sites/mysite";

using var clientContext = new AuthenticationManager()
                             .GetACSAppOnlyContext(siteUrl, clientId, clientSecret);

cc.Load(cc.Web);

await cc.ExecuteQueryAsync(); // no longer throws a 401

Console.WriteLine(cc.Web.Title); // prints my site's title

I tried to use the newer PnP.Core SDK, but I couldn't find any documentation or examples on how to get that package working with an app-only client secret authenticated context. PnP.Framework's API is the cleanest and most reliable that I've found as of yet.

Answer 2

Constructor of ClientContext requires site url including site name.

var clientId = "myClientId";
var clientSecret = "myClientSecret";
var tenantId = "myTenantId";
var authority = "https://login.microsoftonline.com/" + tenantId;
var siteUrl = "https://myorg.sharepoint.com";
var siteName = "MySiteName";

var app = new ConfidentialClientApplicationBuilder
    .Create()
    .WithClientSecret(clientSecret)
    .WithAuthority(authority)
    .WithTenantId(tenantId)
    .Build();

var paramBuilder = app.AcquireTokenForClient(new[] { siteUrl + "/.default" });
var authResult = await paramBuilder.ExecuteAsync();

// authResult has successfully retrieved an access token at this point

var webFullUrl = $"{siteUrl}/sites/{siteName}";
var context = new ClientContext(webFullUrl);

If the site has some prefix

var webFullUrl = $"{siteUrl}/sites/{sitePrefix}/{siteName}";