How Does SSO Works

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Mukesh Swamy
Oct 13, 2023
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Single sign-on (SSO) is a session and user authentication service that permits a user to use one set of login credentials -- for example, a username and password -- to access multiple applications. SSO can be used by enterprises, small and midsize organizations, and individuals to ease the management of multiple credentials.

How does single sign-on work?

Single sign-on is a federated identity management arrangement. The use of such a system is sometimes called identity federation. Open Authorization (OAuth) is the framework that enables an end user's account information to be used by third-party services, such as Facebook, without exposing the user's password.

OAuth acts as an intermediary on behalf of the end user by providing the service with an access token that authorizes specific account information to be shared. When a user attempts to access an application from the service provider, the service provider sends a request to the identity provider for authentication. The service provider then verifies the authentication and logs the user in.

In a basic web SSO service, an agent module on the application server retrieves the specific authentication credentials for an individual user from a dedicated SSO policy server, while authenticating the user against a user repository, such as a Lightweight Directory Access Protocol directory. The service authenticates the end user for all the applications the user has been given rights to and eliminates future password prompts for individual applications during the same session.

Types of SSO configurations

Some SSO services use protocols, such as Kerberos or Security Assertion Markup Language (SAML):

  • In a Kerberos-based setup, once user credentials are provided, a ticket-granting ticket (TGT) is issued. The TGT fetches service tickets for other applications the user wants to access, without asking the user to reenter credentials.
  • SAML is an Extensible Markup Language standard that facilitates the exchange of user authentication and authorizationdata across secure domains. SAML-based SSO services involve communications among the user, an identity provider that maintains a user directory and a service provider.
  • Smart card-based SSO asks an end user to use a card holding the sign-in credentials for the first login. Once the card is used, the user does not have to reenter usernames or passwords. SSO smart cards store either certificates or passwords.

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