How To Implement SSO (Single Sign-on) in Your Application?

When users juggle multiple accounts across various platforms, the demand for seamless authentication experiences has never been higher.

Single Sign-On (SSO) emerges as a solution, simplifying access management while enhancing security. For companies seeking to empower their applications with this functionality, understanding how to implement Single Sign-On correctly is paramount.

In this comprehensive guide, we explore the benefits of Single Sign-On integration and its best practices. We share our expertise on how to implement SSO.

Delve into the knowledge and tools necessary to understand how to implement SSO in web application seamlessly!

What is Single Sign-On?

Single sign-on SSO is an authentication method that allows users to securely authenticate to multiple applications and sites using one set of credentials.

By allowing users to utilize a single set of credentials to access various services, Single Sign-On implementation boosts user convenience and minimizes the need to remember multiple passwords. To enhance user experience and bolster security,  developers can implement SSO for web applications.

With this technology, users can seamlessly access multiple web services with just one set of login credentials.

An effective software implementation plan for Single Sign-On (SSO) integration should encompass thorough planning, stakeholder alignment, robust testing, and seamless deployment to ensure a secure and user-friendly authentication experience.

How Does SSO Work?

SSO is based on setting up a trust relationship between an application, being in the role of a service provider (SP), and an identity provider (IdP), such as OneLogin, Okta, or AuthO, responsible for storing user identification data and verifying their identity. Such trust relationships rely on the principles of public-key cryptography and the exchange of digital certificates between the two parties at the setup stage.

The certificates contain metadata needed for the verification of messages that the identity provider and the service provider will exchange during user authentication so each knows they come from a trusted source. This information includes each party’s public key, issuer info, expiration, and usage purpose.

When trust is established, the service provider can send authorization requests, and the identity provider will return special tokens (assertions or JSON Web Tokens) with user and session data, confirming the user authentication.

Finally, as multiple service providers establish trust with an identity provider, users within an organization can log in once when using one application, and they automatically gain access to other apps without being prompted to log in again on each of them. This happens because it's the identity provider that handles authorization and user sessions, not the service providers.

What Is an SSO Token?

An SSO token is a message that an identity provider sends to the trusted service provider as a response to a successful authentication request. It functions as proof of the user's identity for the service provider and allows the user to access other apps or services without logging in again.

SSO token contains such information as user data (e.g., their user ID, email, role, and access level), token data (e.g., its issuer, issue time, when it becomes valid, expiration time, etc.), and the issuer’s digital signature. The latter is generated with the IdP’s private key, and it proves the source is trusted if it gets verified by the IdP’s public key that the SP has.

Here’s how an SSO token works:

1. When attempting to access an app, the user gets redirected to the identity provider’s page to log in.
2. When the user enters their credentials, IdP validates them and, if this is successful, issues an SSO token to the SP (the app the user is trying to access).
3. The service provider validates the token using the IdP’s public key it received at the trust-establishing stage (the setup and metadata exchange described earlier).
4. If the token is valid, the app gives the user access.

Depending on the underlying SSO authentication protocol, SAML, OAuth 2.0, or OpenID Connect, the token can be in different formats:

• JWT (JSON Web Token) – for OpenID Connect / OAuth 2.0

• SAML Assertion – for SAML-based SSO

How Secure Is SSO?

Security is one of the key features and benefits of the SSO authentication method, making it so widely adopted. It employs trust relationships, encryption, digital signatures, secure communication protocols, token validation and limiting, session management, and other useful security mechanisms. However, to make all this work, SSO must be implemented properly. In this paragraph, we list the security must-haves for SSO integration.

Trust Relationship

As a basic requirement for SSO setup, a trust relationship between an IdP and an SP is established through metadata exchange. These metadata include such information as each party’s entity IDs, public keys, and endpoints, which will enable digital signature validation at a later stage and ensure that only legitimate systems communicate.

Digital Signatures

Based on public-key cryptography, the digital signature is an important aspect that helps ensure the authenticity and integrity of the tokens transmitted from the IdP to the SP. To make this work, the IdP has to sign the token using its private key, and the SP has to verify it using the matching IdP’s public key (received in metadata exchange). If the token is tampered with in transit, the signature will fail, resulting in rejection of the authentication request.

Secure Communication (HTTPS)

All the communication between the user, the IdP, and the SP is carried out over a secure connection, ensured by TLS (Transport Layer Security) – a cryptographic protocol that enables data encryption, integrity, and authenticity. This prevents the token from being intercepted during transit and helps avoid man-in-the-middle (MITM) attacks. 

Token Expiration and Lifetimes

As we’ve mentioned earlier, tokens contain such information as metadata, that is, information about the token itself. These include its lifetime and expiration info. This is important because it informs the system of how long the token is valid and leaves no chance for attackers to reuse the token later, as the SP will  reject expired tokens

Audience and Issuer Validation

These parameters, indicating the token’s issuer ID and recipient data, are also shared in the token’s metadata and help ensure the token was issued by a trusted source and is reaching the right SP. This helps prevent token reuse across different apps or domains.

Extra Security

SSO allows the implementation of additional mechanisms that add an extra layer of security: single logout (SLO) and multi-factor authentication (MFA). SLO provides the feature of centralized logout – the user will be logged out of all the connected systems once they log out from one of them. MFA stimulates the use of a “secondary” system or device for login to check the user’s identity one more time. 

Developer recommendation:

SSO tokens are sent in a redirect or via an authorization code exchange (for OAuth). To reduce any risks and ensure a secure implementation, it is recommended to use an SDK issued by the selected IdP.

Types of SSO

As we’ve mentioned earlier, SSO can be implemented using different underlying protocols. The most widely used ones are SAML (Security Assertion Markup Language), OAuth 2.0, and OIDC (OpenID Connect). Let’s see how they differ.

SAML SSO

SAML (Security Assertion Markup Language) is an XML-based standard for single sign-on that enables federated SSO and is the oldest SSO standard. It is widely supported, mature, and well-tested, making it a reliable and preferred option for enterprise and B2B applications. 

SAML SSO relies on the exchange of messages in XML format between the identity provider and the service provider. The core of the SAML protocol is a SAML Assertion that an IdP issues as proof of successful user authentication. 

From the standpoint of more modern authentication protocols, SAML is quite verbose and complex, making it harder to debug and requiring attention when implementing. You can find a detailed description of the integration of SAML into applications in our guide on SAML single sign-on implementation.

OIDC SSO

OpenID Connect is, in fact, not an independent protocol but an identity layer built on top of the OAuth 2.0 framework. This means that it uses the OAuth mechanics and format (token exchange and auth flow) to implement authentication, since OAuth alone is only used for authorization and is not designed for sharing user identity data. We explain the process of authorization with OAuth 2.0 in our article How to implement OAuth 2.0 protocol into your application.

In OAuth, the communication between the app and the identity provider is based on JSON message exchange. Thus, OIDC acts as an extension of OAuth, adding some identity parameters (openid scope) to the authorization request addressed to the identity provider, such as the user’s personal data, email, address, phone number, etc. Respectively, the identity provider identifies this request as an authentication request and adds an ID token to its response – the JWT (JSON Web Token).

JWT has the form of a compact, URL-safe, base64-encoded string consisting of a header, payload (identity claims: user’s email, name, unique identifier), and a digital signature that ensures security. 

Now, OIDC is also supported by many identity providers and offers great security due to digital signatures. However, since it is more modern and compact (all data in a single token), it is much more common in mobile apps, SPAs, and microservices architectures than SAML.

How to Choose an SSO Protocol?

First of all, developers should decide on how to implement SSO login. This step involves configuring authentication protocols such as OAuth or SAML (Security Assertion Markup Language) to enable seamless access across multiple web applications. While SAML is widely used in enterprise environments, OAuth 2.0 is more prevalent in single sign-on for web applications due to its simplicity and flexibility.

Developers typically integrate their application with an identity provider (IdP) like Okta or Auth0, allowing users to authenticate once and gain access to all connected services without the need for separate logins.

Get tech insights from our blog post about OAuth 2.0 implementation with Passport.js!

Recommendations for Implementation

For most web-based applications, OAuth 2.0 is recommended due to its extensive support and adaptability to various use cases, including mobile and desktop applications. OAuth 2.0 also integrates well with OpenID Connect (OIDC), providing not just authorization but also authentication, making it a comprehensive solution for SSO.

Meanwhile, SAML is often the preferred protocol for enterprise environments, especially those that include legacy applications relying on older technologies. It also supports federated identity, enabling SSO across different company web domains and authentication with multiple independent B2B service providers through a single identity provider, which is particularly favored by large-scale companies.

7 Advantages of SSO

Single sign-on app integration is a widely adopted and already a gold-standard approach to user authentication due to the range of benefits it brings businesses. We’ll cover them in this section.

Improved User Experience 

The most explicit benefit of single sign-on implementation is the convenience for users. In the era when almost every software product requires a login, the elimination of the need to create a new pair of credentials and memorize them immediately makes your application more attractive in terms of usability. With SSO, your users can utilize their Google, Microsoft, or any other existing account with an identity provider to log in quickly and securely.

Increased Productivity

In business environments, time spent on unnecessary tasks is time wasted. Why make employees waste their worktime, and on some occasions, even nerves, coming up with another unique password they won’t remember? And even more efforts – restoring it at the most inconvenient moment ever. Instead, they can concentrate on their actual tasks and bring real value to your business if your corporate apps rely on single sign-on.

Stronger Security

Centralized authentication introduced by SSO fosters password security policies, be it in business or consumer apps. Many users tend to write down their multiple passwords or use password managers that are not always secure enough, thus breaking important security practices. SSO integration helps to avoid such risks, taking off credentials management from the service provider and delegating it to trusted identity providers. It also enables additional authentication methods like MFA (Multi-Factor Authentication), ensuring even stronger security.

Less IT Management

Simplified authentication workflows for users also mean fewer headaches dealing with issues for IT administrators. So, with SSO integrated into your systems, you can free up the IT staff’s time for tasks that are more complex than password resets and account lockouts. Also, user access management, introducing security policies, and account deprovisioning are much easier through centralized authentication.

Reduced Help Desk Need

Single sign-on in web and mobile applications helps remove password-related issues from the list of potential challenges app users may face when using software. Since identity providers are responsible for login and verifying user identity in SSO, software product support should not be bothered about credential creation, reset, or removal.

Regulatory Compliance

Single sign-on authentication protocols are designed with security standards, such as GDPR, HIPAA, or SOC 2,  in mind. This means they have built-in security features (like public-key encryption or secure communication protocols mentioned earlier), which ensure data privacy, provided everything was implemented following the guidelines and recommendations. 

Improved Identity Management

Single sign-on is an integral part of Identity and Access Management (IAM) systems that, in addition to user authentication, provide more features. These include role and access management, account management, and other authentication methods that provide extra security layers, ensure compliance, etc.

How To Implement SSO In 5 Steps?

To integrate SSO into your application, we suggest an approach with five steps that will be mandatory for any application type.

Step 1: Assess Requirements and Choose an SSO Provider

At this stage, you have to ensure that the SSO solution will fit your architecture and security requirements. Start by identifying all your apps and systems that will rely on  SSO authentication. Evaluate your compliance, scalability, and integration needs to understand the SSO protocol that will best fit your use case (SAML, OAuth2, or OpenID Connect). Select an SSO provider (like Okta, Azure AD, Auth0, Google Workspace, or Keycloak).

Step 2: Prepare Identity Infrastructure

Next, you need to create a centralized, secure identity management foundation by making the necessary preparations. For example, connect your Identity Provider (IdP) to a central user directory (Active Directory, LDAP) and standardize user attributes (e.g., email, username, group memberships) for the right role-to-user mapping. You might also want to set up Multi-Factor Authentication (MFA) and strong password policies.

Step 3: Configure the SSO Integration

This step should focus on establishing the trust relationships important for SSO and data flow between your app and the selected IdP. To do this, you’ll need to register your application with the IdP, configure the authentication settings depending on the selected protocol (SAML, OIDC), exchange metadata (like public key or client ID/secret), and, finally, define the user data that needs to be transferred (scopes, claims, and role mappings).

Step 4: Test and Validate

To ensure your authentication workflows are smooth and secure, conduct end-to-end testing of the login, logout, session timeouts, and error handling functionality. Make sure you test for multiple roles, permission levels, and device types. Also, it is important to check logging and audit trails for compliance and traceability.

Step 5: Rollout and Monitor

This is the closing step meant to ensure your SSO solution is well-adopted, reliable, and user-friendly. You can roll out SSO to users or groups gradually to better track the performance, continuously monitoring the key indicators like usage, performance, and security logs. A good practice is to set up alerts for unusual login activity or failed attempts, for enhanced, preventive security. It’s also important to train users on using the solution properly and to carry out clear communication to resolve issues on time.

Technical Implementation Using Java

Integrating SSO into a Java application involves several key steps. The examples below illustrate how to implement SSO with a simplified version, focusing on OAuth 2.0 with OIDC for authentication.

Setting Up Dependencies

First, include the necessary dependencies in your project. For a Spring Boot application, Spring Security makes OAuth 2.0 integration straightforward:

<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-oauth2-client</artifactId>
</dependency>

Configuring OAuth 2.0

In the application.yml (or application.properties), configure the OAuth 2.0 details provided by the identity provider (IdP):

spring:
 security:
   oauth2:
     client:
       registration:
         google:
           clientId: [CLIENT-ID]
           clientSecret: [CLIENT-SECRET]
           scope: profile, email
       provider:
         google:
           authorization-uri: https://accounts.google.com/o/oauth2/auth
           token-uri: https://oauth2.googleapis.com/token
           user-info-uri: https://www.googleapis.com/oauth2/v3/userinfo
           user-name-attribute: sub

This example uses Google as the identity provider but can be adapted for any OAuth 2.0-compliant provider.

Securing Endpoints

Secure application endpoints by configuring security settings. Spring Security simplifies this with Java configuration:

@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

   @Override
   protected void configure(HttpSecurity http) throws Exception {
       http
           .authorizeRequests(authorizeRequests ->
               authorizeRequests
                   .antMatchers("/", "/home").permitAll()
                   .anyRequest().authenticated())
           .oauth2Login();
   }
}

This configuration ensures that the home page is accessible without authentication, whereas other endpoints require the user to be authenticated.

Handling Authentication Tokens

After successful authentication, applications receive an authentication token. Here’s a simple way to use the token to make authenticated requests:

@Autowired
private OAuth2AuthorizedClientService authorizedClientService;

public String getUserName(String clientRegistrationId, Authentication authentication) {
   OAuth2AuthorizedClient client = authorizedClientService.loadAuthorizedClient(
           clientRegistrationId, authentication.getName());

   String userInfoEndpointUri = client.getClientRegistration()
           .getProviderDetails().getUserInfoEndpoint().getUri();

   if (!StringUtils.isEmpty(userInfoEndpointUri)) {
       RestTemplate restTemplate = new RestTemplate();
       HttpHeaders headers = new HttpHeaders();
       headers.add(HttpHeaders.AUTHORIZATION, "Bearer " +client.getAccessToken().getTokenValue());

       HttpEntity<String> entity = new HttpEntity<>("", headers);
       ResponseEntity<Map> response = restTemplate.exchange(userInfoEndpointUri,HttpMethod.GET, entity, Map.class);
       Map userAttributes = response.getBody();
       return (String) userAttributes.get("name");
   }

   return null;
}

This method retrieves the user’s name using the OAuth 2.0 token to authenticate the request to the user info endpoint.

Conclusion

Integrating SSO in Java applications can significantly enhance user experience by simplifying the login process across multiple platforms. While the choice between SAML and OAuth 2.0 depends on specific application needs, OAuth 2.0 with OIDC is generally recommended for its adaptability. We've general the common vision on how SSO is implemented.

Following the outlined steps for a Java-based SSO implementation, developers can ensure a streamlined authentication process, reinforcing both user convenience and security.

Don’t hesitate to contact us to get started and receive a free consultation on how to implement SSO in your app!

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