Identity federation . If you want more control over how users access Office 365, you can set up directory synchronization ...

Identity federation. If you want more control over how users access Office 365, you can set up directory synchronization with identity federation. Identity federation provides a single sign-on (SSO) experience and requires using Active Directory Federation Services (AD FS). This sign-in method ensures all user authentication is managed on-premises and allows administrators to implement more rigorous levels of Office 365 access control. Identity federation with AD FS requires deploying additional servers in your environment. Identity federation also commits you to providing 24x7 support for your Active Directory and AD FS infrastructure. This means that if your on-premises Internet access, domain controller, or AD FS servers are unavailable, your users will be unable to sign in to Office. However, as a backup for infrastructure issues, you can select as an optional feature to enable Password Synchronization.