I need to access Sharepoint through a Java app using Azure AD certificate authentication (https://learn.microsoft.com/en-us/sharepoint/dev/solution-guidance/security-apponly-azuread). The equivalent of this C# sample:

using Microsoft.SharePoint.Client;
using PnP.Framework;
using System;
using System.IO;

namespace AzureADCertAuth
{
    class Program
    {
        static void Main(string[] args)
        {
            var authManager = new AuthenticationManager("00000000-0000-0000-0000-000000000000", "certpath.pfx", "password", "foo.onmicrosoft.com");
            using (var cc = authManager.GetContext("https://foo.sharepoint.com/sites/sitename"))
            {
                cc.Load(cc.Web, p => p.Title);
                cc.ExecuteQuery();
                Console.WriteLine(cc.Web.Title);
                Microsoft.SharePoint.Client.File file = cc.Web.GetFileByUrl("https://foo.sharepoint.com/sites/sitename/docpath.docx");
                ClientResult<Stream> streamResult = file.OpenBinaryStream();
                cc.ExecuteQuery();

                using (StreamReader sr = new StreamReader(streamResult.Value))
                {
                    string fileContents = sr.ReadToEnd();
                }
            }
        }
    }
}

This C# code is working fine for accessing Sharepoint, but I’m having trouble figuring out how to do it in Java.

I tried something like this

import com.azure.core.credential.AccessToken;
import com.azure.core.credential.TokenRequestContext;
import com.azure.core.http.HttpClient;
import com.azure.core.http.HttpMethod;
import com.azure.core.http.HttpRequest;
import com.azure.core.http.HttpResponse;
import com.azure.core.http.okhttp.OkHttpAsyncHttpClientBuilder;
import com.azure.identity.ClientCertificateCredential;
import com.azure.identity.ClientCertificateCredentialBuilder;

import java.net.MalformedURLException;
import java.net.URL;

public class SharepointTest {

    public static void getAccessTokenCert() {
            ClientCertificateCredential credential = new ClientCertificateCredentialBuilder().clientId(
                            "00000000-0000-0000-0000-000000000000")
                    .tenantId("11111111-1111-1111-1111-111111111111")
                    .pfxCertificate("certpath.pfx", "password")
                    .build();
            
            AccessToken token = credential.getToken(new TokenRequestContext().addScopes("https://foo.sharepoint.com/.default")).block();
            
            String url = "https://foo.sharepoint.com/sites/sitename/docpath.docx";
            HttpClient httpClient = new OkHttpAsyncHttpClientBuilder().build();

            HttpRequest request = null;
            try {
                request = new HttpRequest(HttpMethod.GET, new URL(url)).setHeader(
                        "Authorization", "Bearer " + token.getToken()).setHeader("Accept", "application/json;odata=verbose");
            }
            catch (MalformedURLException e) {
                throw new RuntimeException(e);
            }

            HttpResponse response = httpClient.send(request).block();
            String responseBody = response.getBodyAsString().block();
    }
}

But requesting the token throws the following exception:

throwIfFatal detected a jvm fatal exception, which is thrown and logged below:: java.lang.NoClassDefFoundError: io/netty/handler/codec/DefaultHeaders$ValueValidator

Any ideas what I need to do differently?