SharePointOnlineCredentials is raising this error “The sign-in name or password does not match one in the Microsoft account system.”

Question

I have the following code to connect to a site collection:-

            string s = "******8";
            SecureString passWord = new SecureString();
            foreach (var cc in s)
                passWord.AppendChar(cc);
            using (ClientContext context = new ClientContext("https://***.sharepoint.com/sites/***/"))

            {
                try
                {
                    context.Credentials = new SharePointOnlineCredentials("***@***.onmicrosoft.com", passWord);

                    context.Load(context.Web);
                    context.ExecuteQuery();

but on the context.ExecuteQuery(); i am getting The sign-in name or password does not match one in the Microsoft account system... although i am 100% sure that the username/password are correct.. but if i login to the UI using the username i will get a 2-factor authentication, so could this be the issue?

Answer 1

MFA/Modern Auth is the issue. You shouldn't be using a username/password as this will fail with modern auth and is a bad security practice. Instead, register a SharePoint Addin with the appropriate permission and leverage the Client ID/Secret.

https://docs.microsoft.com/sharepoint/dev/sp-add-ins/register-sharepoint-add-ins

Answer 2

For MFA Authentication, please download and install OfficeDevPnP.Core using Nuget:

static void Main(string[] args)  
{  
   string siteUrl = "https://<tenant-name>.sharepoint.com/sites/contosoteam";  
   var authManager = new OfficeDevPnP.Core.AuthenticationManager();  
   // This method calls a pop up window with the login page and it also prompts  
   // for the multi factor authentication code.  
   ClientContext ctx = authManager.GetWebLoginClientContext(siteUrl);  
   // The obtained ClientContext object can be used to connect to the SharePoint site.  
   Web web = ctx.Web;  
   ctx.Load(web, w => w.Title);  
   ctx.ExecuteQuery();  
   Console.WriteLine("You have connected to {0} site, with Multi Factor Authentication enabled!!", web.Title);  
}   

Reference:

Using CSOM To Connect To A SharePoint Site With Multi Factor Authentication Enabled

Or you can create a app password and use this password instead of user password in the code snippet:

Manage app passwords for two-step verification