Single Sign-On (SSO) has become a cornerstone of modern digital authentication strategies. In essence, SSO allows users to access multiple applications and services with a single set of credentials, streamlining the user experience and enhancing security. For IT managers and technicians, implementing SSO effectively can significantly reduce password fatigue, minimize security risks, and improve overall productivity.

This handbook article aims to provide a deep dive into SSO technologies, exploring various implementation scenarios, underlying mechanisms, and best practices. By the end of this guide, you'll be equipped with the knowledge to make informed decisions about SSO deployment in your organization.

1. Scenarios Where SSO is Needed

1.1 Multi-app Ecosystem

Large tech companies often operate diverse portfolios of applications and services. SSO plays a crucial role in unifying these ecosystems:

• Meta: Facebook, Instagram, Messenger, and Threads form a tightly integrated social media ecosystem. Users can seamlessly switch between these platforms without re-authenticating, enhancing engagement and cross-platform interactions.
• Google: The suite including Google Photos, Drive, Maps, and Home devices showcases how SSO can span both web and IoT environments. A single Google account provides access to a vast array of services, from productivity tools to smart home controls.
• Uber: By unifying Uber ride-hailing, UberEats food delivery, and the Uber Drivers app under a single authentication system, the company provides a cohesive experience for both customers and service providers.

In these ecosystems, SSO not only enhances user experience but also allows for more effective data sharing and personalization across services, while maintaining robust security protocols, even if the apps were all built by completely different teams.

1.2 Spin-off Apps and Campaigns

Enterprises frequently launch new initiatives that require rapid development and deployment. This often includes spin-off projects, and prototype testing of new product concepts. In such cases, Single Sign-On (SSO) can be a crucial tool.

For marketing campaigns requiring quick web apps, SSO allows these temporary applications to securely use existing user bases. SSO also streamlines user onboarding for new ventures by tapping into the parent company’s user pool and facilitates prototype testing with a subset of existing users without creating new authentication systems.

Sometimes, the development team of the core app may be too busy to respond quickly to requests for new initiatives, such as a web app for a marketing campaign. Having an SSO infrastructure in place can empower a small development and design team to iterate rapidly.

By implementing SSO, organizations can maintain agility in launching new initiatives while ensuring that user data remains protected and consistent across all touchpoints.

1.3 Super Apps with Mini Programs

The concept of super apps, popularized in Asian markets, is gaining traction globally, with some popular examples including:

• LINE/KakaoTalk: These super apps incorporate messaging, social media, and a vast ecosystem of mini-programs, all accessible through a single login.
• Gojek: In Southeast Asia, Gojek offers ride-hailing, food delivery, news, and financial services within a single app.

Super apps can also be found within enterprise environments, where they offer significant advantages:

• Corporate Portals: Instead of asking staff to install multiple different apps, an enterprise may package various internal tools into a single mobile app. This super app can include systems like HR, inventory management, and communication platforms, all built by different developers or business units.
• Field Service Apps: Companies with mobile workforces, such as maintenance or IT, can bundle multiple tools (scheduling, invoicing, knowledge bases) into one app with SSO. This approach provides employees with seamless access to all necessary resources in one place.

In both cases, services must be accessible on mobile platforms and web browsers. Delivering these services as web apps is cost-effective and ensures they are always up-to-date. However, implementing SSO in super apps presents unique challenges, particularly in managing session states across different mini-programs or web views.

A secure SSO mechanism helps manage sessions across the app suite, allowing for smooth transitions between services while maintaining strict security boundaries. IT professionals must ensure seamless integration between various services to provide an efficient user experience and uphold high security standards.

1.4 App-to-App Authentication

App-to-app (app2app) authentication is becoming increasingly important in mobile ecosystems, as it offers a simpler and faster flow for authentication when the user has already installed and logged into another recognized app on their mobile device. Here are some key use cases:

• Financial Services: Banking apps can authorize fintech apps to access account information, streamlining processes like budgeting or investment management.

This integration allows users to seamlessly manage their finances across multiple platforms within a single application.

Implementing app2app authentication requires careful consideration of security protocols, user consent mechanisms, and data sharing policies. IT managers must ensure compliance with regulations like GDPR or PSD2 when implementing these solutions.

2. How Sessions are Shared Between Services

2.1 Cookies

Cookie-based SSO is one of the most straightforward and essential methods for authenticating users in web applications. It offers several advantages such as:

• Domain-Level Sharing: By configuring cookies at the root domain level (e.g., .example.com), all subdomains can access the same session information, making it easier to manage user sessions across multiple subdomains.
• Secure and HttpOnly Flags: These flags enhance security by restricting client-side access to cookies and ensuring that they are only transmitted over secure channels.
• SameSite Attribute: This attribute helps mitigate cross-site request forgery (CSRF) attacks by controlling how cookies are included with cross-site requests.

2.2 Redirect Flow

You tap "Login" in an app, and it whisks you away to a familiar login page in your browser. After entering your credentials, you're seamlessly transported back to the app, now fully logged in. This smooth back-and-forth dance is known as the "redirect flow" - a typical implementation of Single Sign-On (SSO) technology.

This seamless experience extends across multiple apps. When a new app redirects you to the same login page, you'll often find your session is still active. With just a quick "Continue" tap, you're in - no need to re-enter your credentials.

The redirect flow is crucial for implementing SSO in cross-platform applications and requires secure token exchange mechanisms such as:

• OAuth 2.0 and OpenID Connect: These protocols standardize the authorization and authentication processes, allowing for secure token exchange.
• State Parameter: This prevents CSRF attacks by ensuring the request's integrity throughout the redirect process.
• PKCE (Proof Key for Code Exchange): An additional security layer for mobile and single-page applications to prevent interception of the authorization code.

Here’s an example flow:

1. User clicks "Login" in App A
2. App A redirects to centralized auth server with client_id and redirect_uri
3. User authenticates on auth server
4. Auth server redirects back to App A with an authorization code
5. App A exchanges code for access and refresh tokens
6. App A can now make authenticated API calls

Implementing this flow requires careful coordination between the client application, authorization server, and resource server to ensure secure token handling and validation.

2.3 Shared Container

Imagine this: You download the new shiny app Google just released, and it instantly opens to your personalized dashboard without asking you to log in or provide details. No email entry, no password prompt — just immediate access. Real-life magic.

This is where shared containers come in.

Shared containers provide a native SSO experience on mobile platforms:

• iOS Keychain and App Groups: Allow secure sharing of credentials between apps from the same developer.
• Android AccountManager: Provides a centralized registry of user credentials that can be securely accessed by authorized apps.

This example demonstrates how to securely store and retrieve authentication tokens using the iOS Keychain, which can be shared between apps from the same developer.

3. Choosing the Right SSO Approach

Selecting the appropriate SSO method depends on various factors:

1. Platform Diversity:

   • Web-only: For non-SPA websites, consider cookie-based solutions. For other applications requiring web-specific SSO protocols you can consider using redirect flow.
   • Mixed (Web and Mobile): Implement OAuth 2.0 with OpenID Connect for a standardized approach across platforms.
   • Mobile-only: Utilize platform-specific shared containers or app2app authentication.

2. Security Requirements:

   • High-security environments may require additional factors like biometrics or hardware tokens.
   • Consider implementing FIDO2 standards for passwordless authentication.

3. User Experience:

   • Evaluate the trade-off between security and convenience.
   • Consider implementing step-up authentication for sensitive operations.

4. Regulatory Compliance:

   • Ensure your SSO solution adheres to relevant standards (e.g., GDPR, HIPAA, PSD2).
   • Implement appropriate consent and data sharing mechanisms.

5. Scalability:

   • Choose solutions that can grow with your user base and application ecosystem.
   • Consider cloud-based identity providers for easier management and scalability.

Taking a thoughtful approach to these considerations will not only enhance security but also streamline access across diverse platforms, ultimately supporting a seamless and efficient user experience.

Conclusion

Implementing SSO effectively requires a deep understanding of various technologies and careful consideration of your organization's specific needs. By leveraging the right combination of cookies, redirect flows, shared containers, and app2app authentication, you can create a seamless and secure authentication experience across your entire digital ecosystem.

As you move forward with your SSO implementation, remember to:

• Regularly audit your authentication systems for security vulnerabilities.
• Stay informed about emerging authentication standards and best practices.
• Collect and analyze user feedback to continuously improve the login experience.
• Plan for future expansion of your application ecosystem and how it will integrate with your SSO solution.

By following these guidelines and choosing the appropriate SSO methods for your use cases, you can significantly enhance both the security and usability of your organization's digital services.

This article is part of a multi-part handbook. If you're interested, follow for more upcoming posts about SSO or join our auth-oriented community