Microsoft 365 apps primarily use Microsoft Azure authentication. 

If you are installing Microsoft 365 apps on a new device or using a new browser to sign in to Outlook on the web, you may be asked to authenticate with Two-Step Login as well.

However, when you login to Microsoft 365, you can:

• Check Don't show this again, and
• Select Yes on the Stay Signed In screen. 

When you take these steps and use Microsoft 365 regularly, you will rarely if ever be asked to re-authenticate with either Microsoft Azure or Two-Step Login when using the same device or, in the case of Microsoft 365 web apps, browser.