First- Ensure Office 365 is set for Modern Auth-
- Log in to the Office 365 portal, Edge seems to work the best.
- Admin Centers, Exchange, Classic Exchange Admin Center.
- Hybrid, click "Configure" under Exchange Online Powershell Module.
- Type "Connect-EXOPSSession -UserPrincipalName <your UPN>"
- Get-OrganizationConfig | ft OAuth*
- If it's set to "True", you're good to go, modern auth is enabled.
- If it's set to false- Set-OrganizationConfig -OAuth2ClientProfileEnabled $True
- Give it a couple of hours.
If a user is still getting the basic prompt in outlook-
- Go into control panel, credential manager, delete everything related
- In regedit, go to HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Common\Identity.
- Create a new DWORD named "EnableADAL" and give it a value 1
If that doesn't work-
- Create a new DWORD named "DisableAADWAM" and give it a value 1
- Create a new DWORD named "DisableADALatopWAMOverride" and give it a value 1