The business of authentication

Single Sign On

What is single sign on?

Single Sign On (SSO) (also known as Enterprise Single Sign On or "ESSO") is the ability for a user to enter the same id and password to logon to multiple applications within an enterprise. As passwords are the least secure authentication mechanism, single sign on has now become known as reduced sign on (RSO) since more than one type of authentication mechanism is used according to enterprise risk models.

For example, in an enterprise using SSO software, the user logs on with their id and password. This gains them access to low risk information and multiple applications such as the enterprise portal. However, when the user tries to access higher risk applications and information, like a payroll system, the single sign on software requires them to use a stronger form of authentication. This may include digital certificates, security tokens, smart cards, biometrics or combinations thereof.

Single sign on can also take place between enterprises using federated authentication. For example, a business partner's employee may successfully log on to their enterprise system. When they click on a link to your enterprise's application, the business partner's single sign on system will provide a security assertion token to your enterprise using a protocol like SAML, Liberty Alliance, WS Federation or Shibboleth. Your enterprise's SSO software receives the token, checks it, and then allows the business partner's employee to access your enterprise application without having to sign on.

Single sign on federated authentication also works with your employees. For example, an employee who is trying to access your outsourced benefits supplier to update their benefits information would click on the benefits link on your intranet. Your enterprise's single sign on software would then send a security assertion token to the benefits supplier. The benefits supplier's SSO system would then take the token, check it and grant access to your employee without making them sign on.

Single Sign On Benefits

Single sign on benefits are:
  • Ability to enforce uniform enterprise authentication and/or authorization policies across the enterprise
  • End to end user audit sessions to improve security reporting and auditing
  • Removes application developers from having to understand and implement identity security in their applications
  • Usually results in significant password help desk cost savings
Since the internet is stateless, this means that the single sign on software must check every request by the user's browser to see if there is an authentication policy pertaining to the resource or application the user is trying to access. In a medium to large enterprise, this means that every time the user clicks on a different URL, there is traffic between the user's browser, the web or application servers and the security server. This traffic can become large and cumbersome from a performance perspective. Therefore, most modern single sign on systems use LDAP (Lightweight Directory Access Protocol) directories to store the authentication and authorization policies. The LDAP directories are made for high performance lookups thus addressing the high traffic load. Further, the LDAP directories are often the source for the single sign on system to authenticate against.

Single sign on systems in medium to large enterprises can become a single point of enterprise failure if not properly designed. If the single sign on system goes down but the applications remain up, no user can access any resource or application protected by the SSO system. Many enterprises have experienced this painful condition resulting in productivity loss. Therefore, it is essential that your enterprise single sign on system have a good and well tested failover and disaster recovery design.

Finally, single sign on systems in medium to large enterprises requires good identity data governance. Enterprise security features being offered by the single sign on system is only as good as the underlying identity data. Thus it is critical that all enterprise identity data have good, quick business processes that pick up on any change to the identity such as new identity creation, identity termination or role changes. Without this, enterprise SSO systems are vulnerable to creating enterprise security holes.

101 Things To Know About Single Sign On


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