How to get a list of all users from Office 365 Organization in C# using CSOM?

Question

I've 4000+ users in my Office 365 organization and want to add all those users to my SharePoint subsite in C# using CSOM. I know I can I achieve this using PowerShell Codes, but I want to do it in C# using CSOM. I can add a particular user by the following code, but how to add all 4000+ users in a single code?. Is there any way to iterate a object in a loop which has all 4000+ users in it?

using System;
using System.Security;
using Microsoft.Online.SharePoint.TenantAdministration;
using Microsoft.SharePoint.Client;
namespace Basic_Site_Subsite_Group_User_Creation
{
    class Program
    {
        static void Main(string[] args)
        {
            //Opens the Admin URL 
            using (ClientContext ctx = new ClientContext("https://developer19.sharepoint.com/sites/Created_with_Communication_site"))
            {
                //Authenticating with Tenant Admin
                SecureString password = new SecureString();
                foreach (char c in "password".ToCharArray())
                    password.AppendChar(c);
                ctx.Credentials = new SharePointOnlineCredentials("kailash@kailash.cf", password);
                    Group gru = ctx.Web.SiteGroups.GetByName("subsite1");
                    User use = ctx.Web.EnsureUser("anil@kailash.cf");
                    gru.Users.AddUser(use);
                    ctx.ExecuteQuery();

Answer 1

You can use this if your organisation have a AD(I believe so)

string groupName = "Domain Users";
string domainName = "your domainName";
PrincipalContext ctx = new PrincipalContext(ContextType.Domain, domainName);
GroupPrincipal grp = GroupPrincipal.FindByIdentity(ctx, IdentityType.SamAccountName, groupName);
if (grp != null)
{
     foreach (Principal p in grp.GetMembers(false))
        {
            p.DisplayName //do your action here
        }


    grp.Dispose();
    ctx.Dispose();
}

Answer 2

Referthis project to register your app so you could call graph api to get users from AD.

if (graphServiceClient != null)
                {
                    var users= await graphServiceClient.Users.Request().GetAsync();

When adding the users to SharePoint, would suggest do this batch(submit 100 users in one request to avoid issue).

Fake code:

for(var i = 1; i <= users.Count; i++)
                    {
                        User use = ctx.Web.EnsureUser(users[i].Mail);
                        gru.Users.AddUser(use);
                        if (i % 100 == 0)
                        {
                            ctx.ExecuteQuery();
                        }
                    }