Think of SSO as a master key that unlocks multiple doors. With SSO, a user only needs to authenticate once to gain access to a range of systems and applications—streamlining user experience and reducing the security risk of reused or weak passwords.
What Is SSO?
Single Sign-On (SSO) is an authentication process that allows users to access multiple applications with one set of login credentials (username and password). Instead of logging in separately to every system, users authenticate once with a trusted Identity Provider (IdP), and this identity is trusted across various services, known as Service Providers (SPs).
How SSO Works: A Real-World Example
To better understand the SSO process, let’s walk through a common scenario: logging into LinkedIn using Google as the Identity Provider.
1) User Requests Access
The user navigates to LinkedIn and chooses “Sign in with Google”. This action tells LinkedIn (the Service Provider) that the user wants to authenticate through Google (the Identity Provider).
2) Authentication Request
LinkedIn redirects the user to Google, sending along an authentication request. This request includes details such as the requested resource, the identity of the service, and where the user should be redirected post-authentication.
3) Identity Provider Checks for Active Session
Google receives the request and checks whether the user already has an active session. If so, it skips the login prompt. If not, it proceeds to the next step.
4) User Submits Credentials
Since there’s no active session, the user is asked to enter their Google credentials—typically an email address and password.
5) Identity Provider Verifies Credentials
Google verifies the credentials against its internal user directory. If valid, an authentication token (or assertion) is generated. This token essentially says: “This user is authenticated and here’s proof.”
6) Token Sent to Service Provider
The token is sent back to LinkedIn. This verifies the user’s identity and grants them access to their LinkedIn account—without needing a separate LinkedIn-specific login.
7) Future Access Without Reauthentication
If the user now visits another Service Provider (e.g., GitHub) that also supports “Sign in with Google,” they won’t be asked to log in again. Google detects the existing session and authorizes access automatically.
Under the Hood: SSO Protocols
SSO functions through standard communication protocols that define how the Identity Provider and Service Providers trust and authenticate users. The most common protocols include:
- SAML (Security Assertion Markup Language): Often used in enterprise environments for exchanging authentication and authorization data.
- OAuth: Commonly used for delegated access, where applications can act on a user’s behalf.
- OpenID Connect: Built on top of OAuth 2.0, it adds an identity layer, making it ideal for user authentication.
Why SSO Matters
Implementing SSO offers significant benefits:
- Improved User Experience: Users log in once and gain seamless access across platforms.
- Reduced Password Fatigue: Fewer passwords to remember means less cognitive load.
- Enhanced Security: Centralized authentication makes enforcing security policies easier (e.g., MFA, account lockouts).
- Efficient IT Management: IT teams manage fewer password reset requests and streamline account provisioning.
Final Thoughts
SSO is more than a convenience—it’s a crucial part of a modern security strategy. By consolidating the authentication process and reducing the number of credentials users must manage, organizations can boost security while making life easier for their users.
As reliance on cloud services and SaaS platforms continues to grow, adopting a robust SSO strategy ensures better security hygiene and a smoother digital experience.