Windows Security always asking for sign in to access Outlook

In the Modern authentication flyout that appears, check if Turn on modern authentication for Outlook 2013 for Windows and later (recommended) is enable. 2. Please check the situation after creating a new outlook profile for a specific user. Navigate to Control Panel > Mail > Show Profiles > add a new profile and make it as default. 3.  

https://answers.microsoft.com/en-us/outlook_com/forum/all/windows-security-always-asking-for-sign-in-to/a1200d1b-11e4-4f7f-99eb-32ed7e4f17c8