Share Folder with Guest User without Account with CSOM

[TMBartsch]

I am quite new in CSOM/Sharepoint development and have an interesting task to solve. Unfortunately I don't make as much progress with some details as I would like. A customer of mine wants a secure way to exchange confidential documents. Therefore my idea was to create a folder in Sharepoint for each customer and to share it with the customer as a guest user. So the customer has access to "his" document folder and can upload and download documents there. I can do this manually as well, but I would like to solve this programmatically via CSOM.

The programmatic creation of the folder I have managed so far. Also the file upload is no problem. However, the release of the folder of the customer is problematic. I managed to share the folder so that the customer can log in with his Microsoft account or that the order is released "for everyone".

What I need is a personal release WITHOUT forcing an MS account. An personal link with verification code etc...

This is my code so far. Is this even possible with CSOM?

public static void CreateAndShareFolder(ClientContext context, string folderName, string userEmail)
    {
        var listTitle = "Dokumente";
        var rootFolder = "Testfolder_ROOT/";

        var folder = CreateFolder(context.Web, listTitle, rootFolder + folderName);

        var users = new List<UserRoleAssignment>();        users.Add(new UserRoleAssignment()
        {
            UserId = userEmail,
            Role = Role.Edit,
        });

        var serverRelativeUrl = folder.ServerRelativeUrl;
        var absoluteUrl = new Uri(context.Url).GetLeftPart(UriPartial.Authority) + serverRelativeUrl;

        /* User gets Email, but with "public" Sharing-Link */
        //var userSharingResults = DocumentSharingManager.UpdateDocumentSharingInfo(context, absoluteUrl, users, true, true, true, null, true, true);
        /* User gets Email, but needs an MS-Account to View */
        var userSharingResults = DocumentSharingManager.UpdateDocumentSharingInfo(context, absoluteUrl, users, false, false, true, null, false, true);        context.ExecuteQuery();
    }

    // From Stackoverflow: https://stackoverflow.com/a/22010815/3062062
    public static Folder CreateFolder(Web web, string listTitle, string fullFolderUrl)
    {
        if (string.IsNullOrEmpty(fullFolderUrl))
            throw new ArgumentNullException("fullFolderUrl");
        var list = web.Lists.GetByTitle(listTitle);
        return CreateFolderInternal(web, list.RootFolder, fullFolderUrl);
    }

    private static Folder CreateFolderInternal(Web web, Folder parentFolder, string fullFolderUrl)
    {
        var folderUrls = fullFolderUrl.Split(new char[] { '/' }, StringSplitOptions.RemoveEmptyEntries);
        string folderUrl = folderUrls[0];
        var curFolder = parentFolder.Folders.Add(folderUrl);        web.Context.Load(curFolder);        web.Context.ExecuteQuery();

        if (folderUrls.Length > 1)
        {
            var subFolderUrl = string.Join("/", folderUrls, 1, folderUrls.Length - 1);
            return CreateFolderInternal(web, curFolder, subFolderUrl);
        }
        return curFolder;
    }