Securing your APIs and Applications with SSO: A step-by-step guide

What would happen if a single password compromise gave access to every one of your internal systems, APIs and applications?

For many organisations, that's not a hypothetical question, it's the reality of poor access control. And on the other side of the spectrum, users deal with login fatigue, multiple sessions and constant re-authentication across platforms.

Single Sign-On (SSO) (SSO) offers a way to untangle that complexity. With SSO, users log in once and gain access to all authorised systems whether they’re web apps, internal tools, or exposed APIs. 

This guide explains how SSO works, how to apply it to your environment and how to avoid common implementation mistakes.

What is SSO and how does it work?

Single Sign-On (SSO) is a method of user authentication that allows individuals to access multiple systems, applications or services using a single set of login credentials. Rather than entering separate usernames and passwords for each tool, the user signs in once via a trusted identity provider (IdP), which then authenticates the session across all authorised platforms.

Here’s how it works in practice:

1. The user attempts to access an application.
2. The application redirects them to an identity provider (IdP).
3. The IdP checks the user’s credentials and, if valid, issues a token.
4. This token is then passed back to the application.
5. The application verifies the token and grants access without needing to know or manage the user’s actual credentials.

This process relies on trust between the identity provider and the applications (often referred to as service providers). That trust is governed through standards and protocols that securely transfer identity and access information.

SSO offloads authentication responsibilities to a central system, reducing the attack surface associated with managing passwords across multiple endpoints. By separating the authentication logic from each individual application or API, it simplifies development, strengthens access control and supports consistent security policies across an organisation.

Benefits of implementing SSO for APIs and Applications

The benefits of SSO go beyond convenience, they contribute directly to operational efficiency, stronger security and user satisfaction across systems:

• Unified access control: Instead of managing credentials across every app or service, permissions are centralised. That simplifies audits, access reviews and compliance.
• Better protection against credential misuse: With fewer passwords in circulation, the risk of weak, reused or shared credentials is dramatically reduced. Combined with MFA, SSO strengthens the entire authentication layer.
• Frictionless user experience: Users log in once and access everything they need. This improves productivity, reduces login errors and supports faster onboarding.
• Lower support burden: Password-related help desk tickets are among the most common IT issues. SSO reduces password fatigue and the need for resets, freeing up support teams for higher-value work.
• Consistent API access control: APIs that rely on token validation benefit from central authentication. This ensures that access tokens follow a single policy, with scope limitations and expiry managed from one place.
• Improved traceability and monitoring: Since all sessions and access flows originate from a central IdP, tracking who did what and when becomes more straightforward. This improves visibility for security and operations teams.

By consolidating identity into a single trusted source, organisations can improve both user experience and control. SSO becomes the foundation for scalable, secure digital ecosystems.

When is SSO the right choice?

Single Sign-On is most effective when your organisation needs a unified approach to managing identity and access across multiple systems. These are the most common scenarios where implementing SSO makes strategic and operational sense:

• Multiple internal or cloud applications: If your users access several systems during their daily workflows (such as CRMs, ERPs, HR platforms, or collaboration tools) SSO can reduce friction and eliminate redundant logins.
• API access that requires user authentication: When your APIs expose sensitive data or require secure access by external partners or internal applications, SSO simplifies authentication by issuing access tokens from a central authority.
• Federated access across departments or partners: If you work with third-party users, subsidiaries, or external teams, SSO makes it easier to manage access across organisational boundaries using federation protocols like SAML or OIDC.
• Desire for uniform authentication policies: Centralising authentication allows your organisation to enforce policies like Multi-Factor Authentication (MFA), password expiry rules, or device-level controls consistently across all services.
• Reduction of IT overhead: Managing user accounts in multiple systems increases complexity. SSO reduces the need for separate password resets, manual provisioning and ad-hoc access control.

However, SSO isn’t a universal solution. It should be paired with:

• Granular authorisation controls at the application level
• Monitoring tools to track user and token behaviour
• Session management rules to prevent stale or persistent sessions from being abused

In short, if you’re aiming to improve both user experience and security posture across applications and APIs, SSO is often the right foundation to build upon.

Key components of an SSO architecture

To design and implement a robust Single Sign-On system, it’s essential to understand its core architectural components. Each plays a distinct role in ensuring secure and efficient authentication across applications and services:

Identity provider (IdP)

This is the central authority responsible for authenticating users. It verifies credentials (such as passwords, biometrics, or OTPs) and issues tokens or assertions that confirm the user’s identity. Examples include Azure Active Directory, WSO2 Identity Server, Okta and Auth0.

Service providers (SPs)

These are the applications or services that users want to access. Instead of handling login themselves, they rely on the IdP to confirm user identity. Once a valid token is received, the service provider grants access according to predefined permissions.

Authentication tokens

Tokens such as JWT (JSON Web Tokens) or SAML assertions are cryptographically signed credentials issued by the IdP. They include claims about the user, such as their ID, roles, or session expiry. These are passed to SPs as proof of identity.

Protocols and standards

These define how identity information is exchanged. The most widely used are:

• SAML 2.0: Used primarily for browser-based SSO, particularly in enterprise environments.
• OAuth 2.0: Grants scoped access to APIs without exposing user credentials.
• OpenID Connect (OIDC): Built on OAuth 2.0, this adds an identity layer used for authenticating users and retrieving user profile information.

Trust relationships

The SP and IdP must trust each other. This trust is often established through certificate-based signatures, secure endpoints and shared metadata. Without trust, SSO cannot function securely.

Token validation logic

Each SP must include mechanisms to validate the tokens they receive, checking for:

• Authenticity (signature validation)
• Expiry and time constraints
• Audience restrictions (token was meant for this app)
• Integrity of claims (unchanged data)

Session management

Although the user logs in once, the system must manage how long tokens remain valid, how logout is handled across systems (Single Logout) and what happens when sessions expire.

Together, these components form a secure, scalable architecture that reduces login complexity and enforces consistent authentication across your organisation’s digital assets.

Step-by-step: How to secure your APIs and Applications with SSO

Implementing SSO can feel complex, especially when APIs, web applications, mobile clients and legacy systems are involved. This step-by-step approach will help guide your team through the process in a structured and realistic way:

Step 1: Define the systems and users involved

Create an inventory of:

• Applications (web, mobile, internal)
• APIs (public, internal, third-party integrations)
• User types (employees, external partners, customers)

Understanding these relationships will shape the design of your SSO architecture.

Step 2: Select the appropriate SSO protocol

• Use OpenID Connect (OIDC) for modern applications and web login flows.
• Use OAuth 2.0 for token-based API access and delegated authorisation.
• Use SAML 2.0 if your environment includes older enterprise applications.

Choose a protocol that all components support and that aligns with your security goals.

Step 3: Choose and configure your Identity Provider (IdP)

Select an IdP that integrates with your systems and supports your chosen protocol(s). Consider factors such as:

• Cloud vs. on-premise deployment
• Integration with user directories (e.g., LDAP, Active Directory)
• Support for Multi-Factor Authentication (MFA) and policy enforcement

Popular IdPs include Azure AD, WSO2 Identity Server, Auth0, Okta and Keycloak.

Step 4: Configure applications and APIs to accept identity tokens

Each application or API needs to:

• Trust the IdP (by verifying its public keys or certificates)
• Accept and validate the incoming tokens
• Map token claims to internal roles or permissions

Use standard libraries or SDKs to simplify integration and ensure tokens are properly validated (signature, expiry, issuer, audience).

Step 5: Implement login and logout flows

Ensure your applications can redirect unauthenticated users to the IdP and handle token exchanges securely. Also implement:

• Single Logout (SLO), where supported
• Session timeouts and refresh logic

Step 6: Test the full authentication and authorisation cycle

Run integration tests covering:

• Successful logins
• Role-based access enforcement
• Expired or tampered tokens
• Logout and session termination

Step 7: Monitor and maintain

• Use logs to detect anomalies and track usage
• Periodically review access policies and token lifespans
• Ensure the IdP remains patched and securely configured

With these steps, your organisation can deploy an SSO setup that not only reduces friction but significantly improves access control and visibility.

Common pitfalls and how to avoid them

Even well-planned SSO implementations can encounter serious issues if some fundamental aspects are overlooked. Below are the most common mistakes organisations make and how to avoid them:

• Skipping token validation: Trusting any token without verifying its signature, expiry time, audience and issuer is a critical security flaw. Always validate tokens using libraries compatible with your IdP’s signing method.
• Inconsistent logout behaviour: Many organisations fail to implement proper logout flows across all applications. As a result, users may remain signed in on certain services even after logging out elsewhere. Support Single Logout (SLO) where possible and define session expiration rules clearly.
• Improper use of multiple protocols: Mixing OIDC, SAML and OAuth within the same system can lead to compatibility issues and confusion over token handling. Choose a consistent protocol per use case and document it thoroughly.
• Hardcoding configuration: Credentials, endpoints and certificates should never be hardcoded. Use secure environment variables and centralised configuration management to adapt as systems evolve.
• Token misuse between apps: Reusing tokens across services with different scopes can lead to privilege escalation. Define and enforce specific scopes for each token issued.
• Insufficient user mapping logic: Service providers must correctly interpret token claims and map them to local permissions or roles. Inconsistent mappings can result in access issues or over-permissioned users.
• Lack of monitoring and alerting: Without logging authentication events and token usage, it’s impossible to detect anomalies or troubleshoot issues. Integrate your IdP with observability tools for proactive oversight.

Avoiding these pitfalls requires close coordination between development, operations and security teams. A well-documented, thoroughly tested SSO configuration is the foundation for secure and scalable identity management.

Choosing the right tools for your SSO strategy

Selecting the right SSO tool depends on your organisation's size, infrastructure, regulatory requirements and technical maturity. Here are key factors to consider when evaluating tools:

• Protocol support: Ensure the tool supports the protocols your applications and APIs require (OIDC, OAuth 2.0, SAML).
• Deployment model: Do you need a SaaS-based solution (like Auth0) or prefer to host your IdP on-premise or in your cloud (e.g. WSO2 Identity Server, Keycloak)?
• Integration with your tech stack: Choose a tool that integrates well with your existing applications, user directories (e.g. LDAP, AD) and cloud providers.
• Scalability and performance: Consider authentication throughput, response times and how easily the solution scales with your growth.
• Security features: Look for support for Multi-Factor Authentication (MFA), token revocation, audit trails and session management.
• Customisation and extensibility: Some tools allow deep configuration of login flows, theming, or custom business rules.

Popular options include:

• WSO2 Identity Server: An open-source identity and access management platform. Ideal for organisations needing fine-grained control, protocol flexibility and full on-premise or hybrid deployment.
• Auth0: A developer-friendly SaaS solution that supports OIDC, OAuth 2.0 and SAML. Offers fast integration, good documentation and extensible rule-based authentication.
• Azure Active Directory (Entra ID): Strongly integrated with Microsoft environments. Ideal for businesses already using Microsoft 365 or Azure.
• Okta: A leading identity platform known for enterprise-ready features, strong documentation and ease of use across cloud and hybrid environments.
• Keycloak: A Red Hat-backed open-source IdP with solid community support. Suitable for teams that want full control and prefer containerised deployment (e.g. Kubernetes).

Evaluate each option based on your requirements for support, compliance, control and integration ease. Pilot small, document thoroughly and scale with confidence.

Conclusion

Is your organisation growing, but access management is still stuck in the past? SSO can be the shift that helps you reduce friction, unify control and protect sensitive systems without overcomplicating your user experience.

From APIs and web apps to internal systems and federated partners, SSO enables secure access across your digital estate. But implementing it correctly requires more than tool selection, it calls for strategic planning, deep understanding of protocols and robust integration practices.

Need help implementing SSO in your environment? Our team can guide your organisation through every step from choosing the right protocol to securing your APIs and applications. Contact us now!

Talk to our experts!

Contact our team and discover the cutting-edge technologies that will empower your business.

Get in touch

Mariluz Usero

Share