How Does Single Sign-On Work?

What is Single Sign-On?

Single sign-on (SSO) is an authentication method that enables users to securely authenticate with multiple applications and websites by using just one set of credentials.

How Does SSO Work?

SSO works based upon a trust relationship set up between an application, known as the service provider, and an identity provider, like OneLogin. This trust relationship is often based upon a certificate that is exchanged between the identity provider and the service provider. This certificate can be used to sign identity information that is being sent from the identity provider to the service provider so that the service provider knows it is coming from a trusted source. In SSO, this identity data takes the form of tokens which contain identifying bits of information about the user like a user’s email address or a username.

The login flow usually looks like this:

1. A user browses to the application or website they want access to, aka, the Service Provider.
2. The Service Provider sends a token that contains some information about the user, like their email address, to the SSO system, aka, the Identity Provider, as part of a request to authenticate the user.
3. The Identity Provider first checks to see whether the user has already been authenticated, in which case it will grant the user access to the Service Provider application and skip to step 5.
4. If the user hasn’t logged in, they will be prompted to do so by providing the credentials required by the Identity Provider. This could simply be a username and password or it might include some other form of authentication like a One-Time Password (OTP).
5. Once the Identity Provider validates the credentials provided, it will send a token back to the Service Provider confirming a successful authentication.
6. This token is passed through the user’s browser to the Service Provider.
7. The token that is received by the Service Provider is validated according to the trust relationship that was set up between the Service Provider and the Identity Provider during the initial configuration.
8. The user is granted access to the Service Provider.

When the user tries to access a different website, the new website would have to have a similar trust relationship configured with the SSO solution and the authentication flow would follow the same steps.

What is an SSO Token?

An SSO token is a collection of data or information that is passed from one system to another during the SSO process. The data can simply be a user’s email address and information about which system is sending the token. Tokens must be digitally signed for the token receiver to verify that the token is coming from a trusted source. The certificate that is used for this digital signature is exchanged during the initial configuration process.

Reference

• https://www.onelogin.com/learn/how-single-sign-on-works