Sign in to Microsoft Teams using modern authentication
Microsoft recommends that organizations use recent versions of Windows 10 with either Hybrid Domain Join or Azure AD Join configuration. This ensures that users’ accounts are primed in Windows’ Web Account Manager, which in turns enables single sign-on to Teams and other Microsoft applications. This provides a better user experience (silent sign-in) and a better security posture.
Microsoft Teams uses modern authentication to keep the sign-in experience simple and secure. To see how users sign in to Teams, read Sign in to Teams.
How modern authentication works
Modern authentication is a process that lets Teams know that users have already entered their credentials (like their work email and password) elsewhere, and they shouldn't be required to enter them again to start the app. The experience will vary depending on a couple factors, like if users are working in Windows or on a Mac. It will also vary depending on whether your organization has enabled single-factor authentication or multi-factor authentication (multi-factor authentication usually involves verifying credentials via a phone, providing a unique code, entering a PIN, or presenting a thumbprint). Here's a rundown of each modern authentication scenario.
If users have already signed in to Windows or to other Office apps with their work or school account, when they start Teams they're taken straight to the app. There's no need for them to enter their credentials.
Microsoft recommends using Windows 10 version 1903 or later for the best Single Sign-On experience.
If users are not signed in to their Microsoft work or school account anywhere else, when they start Teams, they're asked to provide either single-factor or multi-factor authentication (SFA or MFA), depending on what your organization has decided they'd like the process to entail.
If users are signed in to a domain-joined computer, when they start Teams, they might be asked to go through one more authentication step, depending on whether your organization opted to require MFA or if their computer already requires MFA to sign in. If their computer already requires MFA to sign in, when they open up Teams, the app automatically starts.
On Domain joined PCs, when SSO isn't possible Teams may pre-fill its login screen with the user principal name (UPN). There are cases where you may not want this, especially if your organization uses different UPNs on-premises and in Azure Active Directory. If that's the case, you can use the following Windows registry key to turn off pre-population of the UPN:
Skipping or ignoring user name pre-fill for user names that end in ".local" or ".corp" is on by default, so you don't need to set a registry key to turn these off.
On MacOS, Teams will prompt users to enter their username and credentials and may prompt for multi-factor authentication depending on your organization's settings. Once users enter their credentials, they won't be required to provide them again. From that point on, Teams automatically starts whenever they're working on the same computer.
Switching accounts after completing modern authentication
If users are working on a domain-joined computer (for example, if their tenant has enabled Kerberos), they cannot switch user accounts once they've completed modern authentication. If users are not working on a domain-joined computer, they can switch accounts.
Signing out of Teams after completing modern authentication
To sign out of Teams, users can click their profile picture at the top of the app, and then select Sign out. They can also right-click the app icon in their taskbar, and then select Log out. Once they've sign out of Teams, they need to enter their credentials again to launch the app.
URLs and IP address ranges
Teams requires connectivity to the Internet. To understand endpoints that should be reachable for customers using Teams in Office 365 plans, Government and other clouds, read Office 365 URLs and IP address ranges.
Teams presently requires access (TCP port 443) to the Google ssl.gstatic.com service (https://ssl.gstatic.com) for all users; this is true even if you're not using Gstatic. Teams will remove this requirement soon (early 2020), and we'll update this article accordingly at that time.
Troubleshooting modern authentication
Modern authentication is available for every organization that uses Teams, so if users are not able to complete the process, there might be something wrong with your domain or your organization's Microsoft work or school account.
For more information, see Why am I having trouble signing in to Microsoft Teams?