Imagine your team in a B2B organization building a product catering to large enterprise companies. These companies have employees navigating various applications accumulated over years of experimentation and success. They already have to remember multiple logins and different application endpoints. Now, your application has been added to the mix, and they have one more login and endpoint to manage and remember. Imagine the plight of that employee who now worries about bad security unless they practice good password hygiene. 

SSO, or Single Sign-on, is the solution. Centralizing the authentication process with a single identity provider reduces the complexity of the user experience while also increasing security.

This SSO blueprint is useful for developers new to setting up SSO in modern applications or needing a quick reference while implementing SSO.

SSO Refresher

SSO is a popular authentication method that enables users to access different applications with a single set of passwords. SSO facilitates the login process and improves security by eliminating the need for users to remember multiple passwords.

With SSO, users can authenticate themselves using a centralized authentication service instead of maintaining separate credentials for each application. 

Concepts

A typical SSO implementation has the following components:

• Identity Provider (IdP): The identity provider stores, manages, and authenticates users and issues access tokens. 
• Service Provider (SP): The service provider is an application the user wants to access that relies on the IdP to validate the user’s identity. In this scenario, this would be your B2B application that aims to simplify the login experience.
• Authentication Token: Issued by IdPs, authentication tokens contain information about the user’s identity.‍
• Federation Protocols: These protocols facilitate the authentication and authorization data exchange between IdPs and SPs. SAML and OpenID Connect are the most popular among these protocols, which we will discuss later.

Common protocols

SSO protocols define the standards and guidelines for cross-application authentication and authorization. Below are the commonly used protocols in SSO:

• SAML 2.0 (Security Assertion Markup Language): An open standard based on XML that allows users to exchange authentication and authorization data. It is frequently used in enterprise setups, particularly for web-based applications. It is a very popular choice to integrate with SaaS applications.
  
• OAuth 2.0 (Open Authorization): An authorization framework that allows applications to gain limited access to user accounts via an HTTP service. It is commonly used for API access and mobile applications. ‍
• OpenID Connect (OIDC): It is an identity layer built on OAuth 2.0 that provides authentication capabilities. It is widely used for modern web and mobile applications, particularly consumer-facing services. OIDC powers popular social logins such as Google and Facebook Sign-In.
  

Learn more in our in-depth SSO guide, which covers its length and breadth.

Blueprint for SSO Implementation

This comprehensive SSO blueprint is intended to serve as the main resource for developers who are responsible for implementing SSO in the application they are working on. It covers the entire SSO deployment process, including technical, security, user experience, testing, and compliance criteria.

Technical

Implementing SSO requires technical expertise. In this section, we delve into the core components of SSO implementation. This includes selecting appropriate protocols (SAML, OAuth 2.0, OpenID Connect), integrating with Identity Providers, handling token validation, and managing user sessions. 

Choosing the right SSO protocol

• Validate your application requirements and choose among SAML or OIDC, the most popular protocols. Both protocols provide a suite of features to manage user authentication.
• Consider your target audience and their typical IdPs. For enterprise clients, prioritize support for popular corporate IdPs like Azure AD or Okta.
• If the organization has an IdP in place, verify the protocols it supports and modify your selection accordingly. For example, WS-Federation may be the preferred choice for Microsoft-centric environments.
• OIDC is usually the best option for mobile apps because of its lightweight design and JSON-based tokens, while SAML and OIDC are both preferable for web applications.
• Consider potential future needs, such as expanding to mobile platforms or integrating with other services.OIDC provides greater adaptability for future growth, particularly in the context of API-driven architectures and mobile devices.

Setting up IdP

• Use language-specific libraries with pre-built components for common SSO protocols, which reduces development time and potential security risks. For instance, use Passport.js for Node.js or Spring Security for Java.
• IdP metadata can be altered and contains critical configuration information, including endpoints, certificates, and SAML/OIDC configuration. Hence, metadata must be encrypted before being saved to a database or secure file storage to ensure its security.
• Enable dynamic client registration for multi-tenant applications to incorporate new tenants into multi-tenant applications without manual intervention.

Setting up SP

Setting up a service provider involves managing authentication tokens and ensuring secure communication between the service and identity providers. 

• Use stateless JWT (JSON Web Token) for improved scalability. JWTs contain all necessary user information, eliminating database lookups. This reduces server load and enables easy horizontal scaling. 
• Implement Proof Key for Code Exchange (PKCE) for all OAuth 2.0 flows. It safeguards public clients (such as single-page apps and mobile apps) from interception attempts. PKCE provides an additional degree of security, guaranteeing that authorization codes are not stolen or misused.
• Implement a "logout everywhere" feature that ensures that when a user logs out of one application, they are also logged out of all other applications to which they are authenticated via the SSO session. This reduces orphan sessions and enhances security.

Security Considerations While Implementing SSO

When implementing SSO, security is one of the key considerations. A few critical steps must be implemented, including the implementation of secure token management, the protection of common vulnerabilities, and the implementation of multi-factor authentication.

Token handling and storage

Token-based authentication is a vital authentication feature, particularly for web applications and APIs. To ensure the application's security, tokens must be stored and managed properly.

• Always validate tokens on the server side. Never trust client-side validation because client-side validation can be easily bypassed and is vulnerable to tampering and exploitation.
• Access tokens should have a short lifespan. When they are set to expire quickly, the risk of a token being compromised is reduced significantly. To counter frequent logins occurring from short-lived tokens, consider using refresh tokens. 
• To prevent any unwanted access, access, or refresh, tokens that are kept in a database should always be encrypted or hashed with salt. This provides an extra layer of security in case the database is compromised. JWT can be used as a stateless token alternative, avoiding the need to store them in the database.

Protect against common vulnerabilities

Protecting against vulnerabilities that are commonly encountered is a fundamental aspect of security.

• Implement  Cross-site Request Forgery (CSRF) protection for SSO endpoints, as these attacks send unexpected requests to the user's browser. Using unique CSRF tokens for every session can prevent attackers from carrying out unauthorized actions on behalf of authenticated users.
• Users exchange credentials for tokens at token endpoints, which are the primary targets of brute-force attacks. Implementing rate limiting on token endpoints can help prevent these types of attacks.
• Cross-origin Resource Sharing policies manage who can access resources. Implementing strict CORS policies can prevent requests from unauthorized domains, lowering the risk of cross-origin attacks.
• Any endpoints accessed, such as metadata URLs, should be validated against Server Side Request Forgery (SSRF)  Attacks. 
• WAF / Firewall should be employed to prevent DDoS Attacks or Bots trying to brute-force login attempts. 

Implement MFA

Multi-Factor Authentication or MFA, is a layer of security that goes beyond a username and password. It offers an additional level of verification before authorizing users' access. Learn more about MFA in our passwordless authentication guide.

• Offer app-based time-based One-Time Password (TOTP) as a user-friendly MFA option as they are a secure and user-friendly way to implement MFA. Additionally, these applications generate a time-sensitive code that users must input during the login process, which serves as an additional layer of security besides the standard usernames and passwords.
• Encouraging users to set up multi-factor authentication (MFA) during their initial enrollment will ensure their security from the beginning. This minimizes the risk of account compromise before enabling MFA.
• Implement risk-based authentication to trigger MFA selectively. This authentication type determines whether to request MFA based on the user's location, device, and/or behavior.

User Experience 

Regarding SSO, user experience is essential for ensuring a quick, easy, and safe login process. An intuitive SSO system improves not only security but also user satisfaction and acceptance rates.

Designing intuitive flow

The intuitive SSO flow design simplifies and smoothes the login experience, allowing users to seamlessly log in using a single set of credentials across different applications or services without remembering the credentials for each. 

• Ensure that Identity Provider options—like Azure, Google, and other social IdP login options—are visible to users upon arrival at the login page to minimize confusion during the login process.
• Implement a "remember me" feature for returning users. This saves users' login session preferences, allowing them to re-authenticate without entering their credentials each time.

Handling errors & user feedback

Proper management of errors and user feedback during the SSO process is essential for maintaining user trust and reducing frustration.

• Provide clear, non-technical error messages for common SSO issues rather than providing technical error messages and jargon. Use phrases like "We were unable to connect to your company's login service." or "Your session has expired. Please log in again to proceed.”
• If SSO is unsuccessful, it is essential to offer users an alternative method of authentication, such as using a password or a different authentication provider, to ensure that they can continue to access their accounts.
  

Read more tips in our comprehensive UI/UX guide for SSO to design secure SSO flows that provide the ultimate user experience.

Testing & QA

Quality Assurance (QA) and testing ensure that the application performs as expected and follows predefined standards. It consists of several layers of testing, ranging from evaluating individual components to ensuring smooth integration between systems, enhancing reliability and performance.

Unit & integration testing

Unit testing evaluates individual components or functions in isolation to ensure that they work properly. Integration testing ensures that several modules operate together as intended. 

• OAuth-based applications can use tools like `mock-oauth2-server` to replicate OAuth servers and test authentication flows. This library creates a local OAuth server, allowing you to test OAuth-based authentication flows without needing a real IdP. 
• By mocking IdP responses, it is possible to test individual functions that depend on authentication without directly connecting to an actual IdP. It verifies that certain login schedules, token generation, and validation logic perform as expected in a controlled environment.
• An integration test IdP can replicate how authentication works in the real world. This configuration helps to ensure that your system correctly interfaces with an actual OAuth server, including token exchange, login, and user information flow.
• Successful login scenarios should be tested against your customers' most popular IDPs. 

Simulate different scenarios

Conducting tests in various scenarios ensures the system's resilience by verifying its performance in unusual or severe circumstances.

• Test with expired tokens, invalid signatures, and missing claims. You can test the authentication system's resilience and ability to handle faulty or defective tokens using expired tokens, manipulated signatures, and incomplete claims.
• Testing the system's response to slow network conditions and Identity Provider downtime is essential for ensuring it can effectively manage such failures and recover without causing any disruptions.
• SSO systems should be tested for performance under high loads. Simulating large numbers of concurrent users authenticating simultaneously ensures that the system can expand and operate well during peak traffic without performance degradation.

Monitoring

Monitor multiple aspects of the SSO flow, from individual authentication attempts to overall system performance. Several methods exist for evaluating and analyzing the SSO process, as listed below.

Logging events

Logging facilitates the capture of detailed records of system events for auditing and troubleshooting purposes. Effective logging provides visibility into SSO attempts, potential difficulties, and unusual activities while protecting user privacy.

• Logging every Single Sign-On attempt, whether successful or unsuccessful, is critical for creating audit logs and detecting security breaches. Personal Identifiable Information (PII) should be masked to meet privacy standards and prevent sensitive data from being exposed.
• Structured logging builds log entries consistently to make them easier to search, parse, and analyze. This strategy streamlines the detection of patterns or problems in authentication processes, allowing logging systems to process them more efficiently.
• Implementing Open Telemetry for SSO systems ensures that all observability data is consistent, allowing for more accurate diagnostics and insights across the authentication system's multiple components.

Setting up alerts

Setting up alerts allows administrators to be notified of potential issues or anomalies in real-time in the SSO application before they affect users. Alerts can be set for various reasons, some of which are mentioned below:

• Alerts can be configured to notify admins when there is an unusual rise in unsuccessful SSO attempts, which could signal an attack or a technical problem. Monitoring usage trends might also indicate potential setting errors or unlawful acts.
• Monitoring the IdP and setting up alerts for downtime or performance degradation allows the system to address user authentication issues quickly.

Tracking performance

Identifying bottlenecks, evaluating adoption rates, and ensuring a seamless user experience as the application develops are all facilitated by monitoring the performance of SSO systems.

• Monitoring the number of users who adopt SSO over time allows administrators to optimize the authentication process or address adoption barriers, thereby providing valuable insights into the system's usage.

Compliance

Compliance in terms of SSO ensures that data is protected, privacy is being followed, and application is secured utilizing legal, regulatory, and industry-specific criteria and requirements being followed.

Meeting industry standards

Compliance with industry standards such as GDPR and HIPAA ensures that sensitive data is protected and the system operates within legal frameworks. Failure to satisfy these criteria may lead to data breaches and legal consequences.

• Implement GDPR-compliant Data Management Practices for users in the European Union. Implementing GDPR-compliant management of SSO data ensures that personal information, including login credentials, is securely stored and used in accordance with data protection requirements.
• Ensure HIPAA compliance for healthcare applications to secure the privacy and security of Protected Health Information (PHI) during the authentication process so that users can access sensitive medical data. HIPAA compliance for SSO is maintained.

Follow best practices

Ensuring that the SSO system is secure, up-to-date, and reliable while minimizing vulnerabilities and aligning the system with evolving standards can be accomplished by maintaining or adopting a few best practices. 

• Update SSO Libraries and Dependencies Regularly: Outdated libraries and dependencies create security risks. SSO libraries are updated regularly to include the latest security patches and improvements, reducing authentication flow vulnerabilities.
  
• Follow SSO Protocol and Standard Changes: SSO protocols (such as OAuth, SAML, and OpenID Connect) evolve with time. By maintaining a current understanding of the changes and enhancements in these standards, you can ensure that your system is secure, compliant, and compatible with other services.
  
• User Authorization and Transparency: Trust in SSO systems, which handle sensitive data, requires user consent and transparency. Ensure users know how their information is collected, employed, and kept safe.
  
• Compliance from Third-Parties: Third-party service integration into an SSO system requires careful verification that those services likewise follow the same security and regulatory rules as the main system. Third-party non-compliance or a security breach might compromise the entire SSO system.
  
• Regular Audits and Assessments: Regular internal and external audits help ensure that the SSO system and the organization continue to meet industry standards and regulations. Audits are crucial to identifying vulnerabilities in security, compliance issues, and opportunities for improvement.

Following these compliance guidelines helps businesses ensure their SSO systems offer convenience and protect the best standards of security and data protection. 

Troubleshooting Common Pitfalls

When implementing SSO, various issues may arise, including browser compatibility and integration issues. To overcome these challenges, logging methods, debugging tools, and creative workarounds are required to keep functionality consistent even during outages.

SSO integration issues

SSO integration can be challenging because several protocols like SAML, OAuth, or OpenID are involved. Troubleshooting such calls requires both specific tools and a systematic approach.

• Whether at authentication, redirection, or token exchange, tools like SAML-tracer or OAuth debug logs can help find where the SSO process is failing. 
• By enabling detailed logging, it is possible to identify any failures or delays in the authentication sequence, as each stage of the SSO flow is monitored.

IdP downtime

The authentication flow can be interrupted by IdP downtime, making users unable to log in. Fallback mechanisms and caching strategies are used to maintain a certain level of user access.

• Implement a circuit breaker to fall back to local auth only when the IdP is down or unresponsive. A circuit breaker detects the situation and changes to local authentication, thus ensuring that users can continue to access the system without depending on the external IdP.
• Caching user profiles and session information enables the system to provide limited functionality even when the IdP is unavailable, avoiding a complete service outage.

Browser compatibility

Browser compatibility issues can result in inconsistent SSO experiences across various platforms. Due to variations in the way browsers manage cookies, authentication protocols, and security settings, SSO flows may exhibit varying behaviors across different browsers. Thorough testing and understanding of browser policies are required to ensure smooth SSO functionality. 

• Thorough browser testing across all platforms is required for better SSO implementation. Ensuring browser compatibility across Chrome, Firefox, Safari, and mobile versions prevents browser-specific access issues.
• Some browsers disable third-party cookies, which can disrupt SSO functionality. In addition, recent modifications to browser settings about third-party cookies could affect SSO functionality. To ensure a consistent browser experience, these policies must be known.

Summary

While implementing SSO might seem like an extensive task, it's easier to break it down into manageable steps. These steps include choosing the right protocol, following best practices for security, better user experience, and testing. SSO isn't just a technical feature; it's also a way for users to have a safer and smoother experience. An SSO solution set up correctly makes things safer and easier to log in, so users can focus on what's important without having to do a lot of logins.

This SSO blueprint covered topics such as understanding common SSO concepts, selecting the right protocol, and setting up IdP and SP. Implementing strong security measures, conducting extensive testing and quality assurance, effectively monitoring and logging, ensuring compliance, troubleshooting Common SSO issues, and so on. It is important to remember that although this blueprint provides you with a solid roadmap, each project may present its unique challenges.

By using this blueprint, you can make SSO implementations that are safe, quick, and easy for users to understand. This will improve both the security and user experience in your apps.