Quick post about a problem I had connecting SharePoint Designer 2013 to SharePoint Online with Modern Authentication.

The login screen would keep prompting for a login but not accept the username and password that worked when connecting via a browser.

The fix is to add the following registry key entries to enable modern authentication on Office 2013 applications.

[HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common\Identity]

“Version”=dword:00000001
“EnableADAL”=dword:00000001

Full details here:

https://support.office.com/en-us/article/Enable-Modern-Authentication-for-Office-2013-on-Windows-devices-7dc1c01a-090f-4971-9677-f1b192d6c910