Single Sign-On (SSO) Explained

A Comprehensive Guide to SSO: Providers, Flows, and Benefits

Key Takeaways

Simplified Access: SSO allows users to access multiple applications with a single set of credentials, eliminating the need for repeated logins.
Two Primary Flows: SSO operates through either Identity Provider (IdP)-initiated or Service Provider (SP)-initiated flows, each with distinct starting points.
Enhanced Security and Efficiency: SSO improves user experience, reduces password fatigue, and provides centralized access management.

What is Single Sign-On (SSO)?

Single Sign-On (SSO) is an authentication method that enables users to access multiple applications and services with a single set of login credentials. Instead of managing separate usernames and passwords for each application, users authenticate once and gain access to all authorized systems seamlessly. This approach enhances user experience, reduces password fatigue, and improves security by minimizing the number of credentials in use.

How Does SSO Work?

SSO operates within a federated identity framework, where an Identity Provider (IdP) authenticates the user and asserts their identity to various Service Providers (SPs). The typical SSO process involves the following steps:

User Initiates Access

The user attempts to access a Service Provider (SP), such as an application or website.
Redirection to Identity Provider

If the user is not already authenticated, the SP redirects the user to the IdP for authentication.
User Authentication

The IdP prompts the user to enter their credentials (if not already authenticated).
Assertion of Identity

Upon successful authentication, the IdP sends an assertion (often via SAML or JWT tokens) back to the SP, confirming the user's identity.
Access Granted

The SP grants access to the user based on the received assertion, allowing seamless entry without additional login prompts.

Key Components of SSO

SSO systems rely on several key components working together:

Identity Provider (IdP)

The IdP is the entity responsible for authenticating the user and providing the necessary identity information. It manages user identities and credentials. Examples include Okta, Microsoft Entra ID (formerly Azure AD), OneLogin, Google Workspace, and AWS IAM Identity Center.
Service Provider (SP)

The SP is the application or service that the user wants to access. The SP relies on the IdP for user authentication. Examples include Salesforce, Google applications, and other web-based services.
Authentication Tokens/Assertions

These are secure credentials passed between the IdP and SP to verify the user's identity. Common formats include SAML (Security Assertion Markup Language) and JWT (JSON Web Tokens).

SSO Flow Types

There are two primary types of SSO flows:

1. Identity Provider (IdP)-Initiated Flow

In this flow, the user first logs into the IdP. After authentication, the user requests access to a Service Provider through an SSO portal. The IdP initiates an SSO connection and sends an assertion (containing the user's identity, attributes, and entitlements) to the SP. The SP then grants access based on the assertion information. This flow is often used in environments where users start their session from a centralized portal.

2. Service Provider (SP)-Initiated Flow

In this flow, the user attempts to access the SP directly. If the user is not already authenticated, the SP redirects the user to the IdP for authentication. The IdP authenticates the user and generates a response (often in SAML format) that is sent back to the SP. The SP verifies this response and grants access if it is valid. This is common when accessing a specific application directly.

Visualizations of SSO Flows

1. Service Provider (SP)-Initiated SSO Flow

The following diagram illustrates the SP-initiated flow:


[User] --> [Service Provider (SP)] : Access Application
[SP] --> [User's Browser] : Redirect to IdP for Authentication
[User's Browser] --> [Identity Provider (IdP)] : Request Authentication
[IdP] --> [User's Browser] : Authentication Prompt
[User's Browser] --> [IdP] : Submit Credentials
[IdP] --> [User's Browser] : Send SAML/JWT Assertion
[User's Browser] --> [SP] : Forward Assertion
[SP] --> [User] : Grant Access to Application

2. Identity Provider (IdP)-Initiated SSO Flow

The following diagram illustrates the IdP-initiated flow:


[User] --> [Identity Provider (IdP)] : Log into Central Portal
[IdP] --> [User's Browser] : Provide Access Options to SPs
[User] --> [IdP] : Select Application to Access
[IdP] --> [User's Browser] : Send SAML/JWT Assertion to SP
[User's Browser] --> [SP] : Forward Assertion
[SP] --> [User] : Grant Access to Application

Detailed Step-by-Step Example: SP-Initiated SAML Flow

Here's a more detailed breakdown of the SP-initiated flow using SAML:

User Request

The user attempts to access a Service Provider (SP), such as a Salesforce application.
Redirect to IdP

The SP detects that the user is not authenticated and sends a SAML authentication request to the Identity Provider (IdP).
Login at IdP

The IdP authenticates the user, typically through a username and password or other authentication methods.
SAML Response

The IdP generates a SAML assertion containing the user's identity information and sends it back to the SP.
Access Granted

The SP verifies the SAML assertion and, if valid, grants the user access to the requested application.

Common SSO Providers

Several providers offer SSO solutions, each with unique features and integration capabilities:

Provider	Description
Okta	Provides a comprehensive SSO platform supporting various authentication protocols like SAML, OAuth, and OpenID Connect. It offers integrations with thousands of applications and robust security features.
Auth0	A flexible identity platform that supports SSO through multiple protocols. It emphasizes developer-friendly features and customizable authentication flows.
OneLogin	Offers SSO services with strong security measures, including multi-factor authentication (MFA), and supports a wide range of applications and integrations.
AWS Single Sign-On (IAM Identity Center)	Part of Amazon Web Services, it allows centralized access management across AWS services and integrated third-party applications.
Microsoft Entra ID (formerly Azure AD)	Provides enterprise-grade SSO capabilities, integrating seamlessly with Microsoft’s ecosystem as well as numerous third-party applications.
Google Workspace	Offers SSO for Google services and integrates with many external applications, facilitating easy access management for organizations using Google’s ecosystem.
Ping Identity	Provides enterprise-grade identity and access management solutions, including SSO, with a focus on security and scalability.

Benefits of Using SSO

Implementing SSO offers numerous advantages:

Improved User Experience

Users enjoy seamless access to multiple applications without repetitive logins, enhancing productivity and satisfaction.
Enhanced Security

Reduces the risk of password fatigue, encourages stronger password practices, and allows centralized monitoring of authentication. It also minimizes the number of credentials in use, reducing the attack surface.
Simplified Administration

Streamlines user provisioning and deprovisioning, ensuring that access rights are consistently managed across all applications. Centralized management reduces administrative overhead.
Cost Efficiency

Lowers IT support costs related to password resets and account management. Reduced help desk calls related to login issues contribute to cost savings.

Disadvantages of SSO

While SSO offers many benefits, there are also some potential drawbacks to consider:

Single Point of Failure

If the IdP is compromised, all services that rely on it are affected. This makes the IdP a critical component that requires robust security measures.
Setup Complexity

Implementing and configuring SSO can be complex, especially in large organizations with diverse applications. Careful planning and configuration are required for successful deployment.

Conclusion

Single Sign-On is a critical component in modern identity and access management strategies, providing both users and organizations with enhanced security, efficiency, and convenience. By leveraging trusted SSO providers and understanding the underlying authentication flows, businesses can ensure secure and seamless access to their digital resources. SSO not only simplifies the user experience but also strengthens the overall security posture of an organization.