How can I access SharePoint files via a C# web api that uses no user authentication?

Question

I have followed numerous guides on how to access SharePoint via C# and no matter what I do I end up with a "401 Unauthorized response:" I am out o fideas. Anybody able to help? Would prefer working code examples.

using Microsoft.Identity.Client;
using Newtonsoft.Json.Linq;
using System.Net.Http.Headers;

namespace SharePointRestApiExample
{
    class Program
    {
        static async Task Main(string[] args)
        {
            string siteUrl = "https://mydomain.sharepoint.com/sites/mysite";
            string clientId = "client id from app registration";
            string clientSecret = "client secret from app registration";
            string tenantId = "tenant id from my instance";
            string authority = $"https://login.microsoftonline.com/tenant id from my instance";
            string[] scopes = new string[] { "https://mydomain.sharepoint.com/.default" };
            string folderUrl = "/sites/mysite";
			var cca = ConfidentialClientApplicationBuilder.Create(clientId)
            .WithClientSecret(clientSecret)
            .WithAuthority(new Uri(authority))
            .WithRedirectUri("https://localhost")
            .Build();
	        try
    	    {
            var authResult = await cca.AcquireTokenForClient(scopes).ExecuteAsync();
            string accessToken = authResult.AccessToken;
            using (var httpClient = new HttpClient())
            {
                httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
                httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                var response = await httpClient.GetAsync($"{siteUrl}/_api/web?select=Title");
                if (!response.IsSuccessStatusCode)
                {
                    string responseContent = await response.Content.ReadAsStringAsync();
                    Console.WriteLine($"Failed to retrieve site info: {response.StatusCode}. Server response: {responseContent}");
                 }
                else
                {
                    string jsonResponse = await response.Content.ReadAsStringAsync();
                    JObject json = JObject.Parse(jsonResponse);
                    string title = json["d"]["Title"].ToString();
                    Console.WriteLine($"Site Title: {title}");
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
    }
}

Answer 1

Hi @David Finkelstein,

To use the REST capabilities that are built into SharePoint, you construct a RESTful HTTP request by using the OData standard, which corresponds to the client object model API you want to use. The client.svc web service handles the HTTP request and serves the appropriate response in either Atom or JSON format. The client application must then parse that response. Please refer to following document

https://learn.microsoft.com/en-us/sharepoint/dev/sp-add-ins/complete-basic-operations-using-sharepoint-rest-endpoints#reading-data-with-the-sharepoint-rest-interface

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