Single Sign-On (SSO) is an authentication method that allows users to access multiple applications and services after signing in through a trusted identity provider. Instead of maintaining separate login credentials for every application, users authenticate once and can access connected applications without repeatedly entering their credentials.
For organizations managing multiple cloud applications, SaaS platforms, internal systems, and business tools, SSO can simplify authentication while giving IT teams a centralized way to manage user access and security policies.
But what is Single Sign-On, how does SSO work, and what technologies make it possible?
This guide explains how SSO works, its components, protocols, benefits, security risks, implementation considerations, and how it differs from related identity technologies.
What Is Single Sign-On (SSO)?
Single Sign-On is an authentication method that allows a user to access multiple trusted applications after authenticating through a central identity system.
The central system is known as an Identity Provider (IdP). The application the user wants to access is known as the Service Provider (SP).
Instead of each application independently asking the user for a username and password, the application can rely on the identity provider to authenticate the user.
For example, an employee may sign in to their organization's identity portal in the morning. After authentication, they can access applications such as their CRM, HR system, collaboration tools, cloud storage, and other connected services without manually entering their credentials for every application.
SSO is therefore more than simply using the same username and password across multiple applications. A true SSO implementation establishes a trusted relationship between the identity provider and the applications and uses an authentication protocol to communicate the user's identity.
Common technologies used with SSO include SAML, OpenID Connect (OIDC), OAuth 2.0, and Kerberos, depending on the application and environment.
How Does Single Sign-On Work?
At a high level, SSO works through a trust relationship between an Identity Provider and one or more Service Providers.
The identity provider is responsible for authenticating the user. The service provider relies on the identity provider's authentication result before establishing an application session.
The exact process depends on the protocol being used, but a typical SSO flow looks like this:
Step 1: User Attempts to Access an Application
The user opens an application or website that supports SSO.
The application acts as the Service Provider (SP). If the user does not already have an active session, the application starts the authentication process.
Step 2: The Application Redirects the User to the Identity Provider
The Service Provider directs the user's browser to the organization's Identity Provider.
Depending on the implementation, the request may contain information identifying the application and the authentication request being made.
Step 3: Identity Provider Authenticates the User
The Identity Provider checks whether the user already has an authenticated session.
If the user has not authenticated, they may be asked to provide their credentials.
The organization may also require additional security controls, such as:
- Multi-factor authentication (MFA)
- Passwordless authentication
- Passkeys
- Device verification
- Conditional access
- Risk-based or adaptive authentication
If authentication succeeds, the identity provider generates the information required by the application to establish trust in the user's identity.
Step 4: Identity Provider Sends an Authentication Response
The identity provider sends an authentication response back toward the Service Provider.
The format depends on the protocol being used.
For example:
- SAML commonly uses a signed SAML assertion.
- OpenID Connect uses an ID token.
- Other architectures may use different tokens or authentication mechanisms.
The response can contain information such as the authenticated user's identity and relevant attributes.
Step 5: Service Provider Validates the Response
The Service Provider validates the response before granting access.
Depending on the protocol, this can involve checking:
- Digital signatures
- Issuer
- Audience
- Timestamps
- Token or assertion validity
- Required claims or attributes
The application should only accept authentication information that meets the trust and security requirements established during configuration.
Step 6: User Gets Access
Once the response has been successfully validated, the Service Provider creates an authenticated session for the user.
The user can then access the application without entering another application-specific password.
When the user opens another connected application, that application can use the same trusted identity provider. If the user already has an active identity-provider session, another interactive login may not be necessary.
This is what creates the experience commonly described as "sign in once."
What Are the Core Components of SSO?
A typical SSO environment contains several components that work together.
Identity Provider (IdP)
The Identity Provider authenticates users and provides trusted identity information to applications.
Examples of identity platforms that can act as IdPs include Microsoft Entra ID and Okta.
The IdP can also enforce security policies such as MFA, conditional access, device requirements, and passwordless authentication.
Service Provider (SP)
The Service Provider is the application or service the user wants to access.
Examples include:
- CRM systems
- HR applications
- SaaS platforms
- Cloud storage
- Collaboration tools
- Internal business applications
The SP relies on the identity provider to authenticate the user rather than maintaining a completely independent authentication process.
User Directory
A user directory stores information about users, groups, and identity attributes.
Enterprise environments may use directories such as Active Directory or LDAP alongside cloud identity platforms.
Directory information can help organizations determine which applications users should be able to access.
SSO Portal
Many enterprise SSO implementations provide users with an application portal where they can see the applications they are authorized to access.
Instead of remembering individual application login pages, users can select an approved application from the organization's SSO portal.
Authentication Tokens and Assertions
Tokens and assertions carry authentication information between trusted systems.
For example, SAML uses assertions, while OpenID Connect uses ID tokens.
These mechanisms allow the Service Provider to receive information about the authentication performed by the Identity Provider.
Trust Relationship and Certificates
SSO depends on establishing trust between participating systems.
During configuration, the IdP and SP exchange information such as metadata, endpoints, identifiers, and certificates.
Digital signatures and certificates can help the Service Provider verify that authentication information originated from a trusted identity provider and has not been altered.
What Is an SSO Token?
An SSO token is information generated or provided as part of an authentication process that allows a system to communicate information about an authenticated user.
The exact form of the token depends on the protocol.
For example, a SAML implementation uses a SAML assertion, while OpenID Connect uses an ID token.
A token may contain information such as:
- User identifier
- Email address
- Authentication information
- Issuer
- Audience
- Relevant user attributes
- Validity information
The Service Provider validates the received information before creating a session for the user.
It is important to distinguish an authentication token from the user's password. SSO does not mean that a user's password is simply copied and passed between applications.
What Protocols Are Used for SSO?
SSO is not a single protocol. Different protocols can provide authentication or related identity capabilities depending on the application architecture.
SAML
Security Assertion Markup Language (SAML) is an XML-based standard widely used for enterprise web SSO.
SAML allows an Identity Provider to communicate authentication and user information to a Service Provider through a SAML assertion.
SAML 2.0 is widely used for enterprise and SaaS application federation.
OpenID Connect (OIDC)
OpenID Connect is an authentication protocol built on top of OAuth 2.0.
OIDC is commonly used by modern web and mobile applications and provides information about the authenticated user through ID tokens.
It is particularly common in newer application architectures.
OAuth 2.0
OAuth 2.0 is primarily an authorization framework, rather than an authentication protocol.
It allows applications to obtain limited access to resources on behalf of a user without requiring the application to receive the user's password.
OAuth and SSO are therefore related but should not be treated as the same technology.
Kerberos
Kerberos is a network authentication protocol commonly associated with enterprise and on-premises environments.
It uses tickets to authenticate users and services without repeatedly transmitting passwords across the network.
Kerberos can support SSO experiences within environments such as Windows-based enterprise networks.
What Are the Different Types of SSO?
SSO can be implemented in different environments and architectures.
Enterprise SSO
Enterprise SSO provides employees with centralized access to business applications through an organizational identity provider.
Federated SSO
Federated SSO allows trusted identity relationships to extend across different organizations, domains, or security environments.
This can allow users from one organization to access resources belonging to another organization without maintaining separate credentials.
Social Single Sign-On
Allows users to sign in using an existing identity from a consumer identity provider, such as a social or personal account.
Cloud-Based SSO
Cloud-based SSO provides centralized authentication for cloud and SaaS applications through an identity provider hosted in a cloud environment.
On-Premises SSO
On-premises SSO operates within an organization's own infrastructure and can be useful for environments with legacy applications or specific infrastructure and compliance requirements.
Passwordless SSO
Passwordless SSO combines the SSO experience with authentication methods such as passkeys, security keys, or other phishing-resistant authentication methods.
SSO vs Password Managers: Are They the Same?
SSO and password management are sometimes confused because both can reduce the number of passwords users need to manually enter.
However, they work differently.
A password manager stores credentials for different applications and can automatically fill those credentials when the user visits an application.
With SSO, the application establishes a trusted relationship with the organization's identity provider. The application does not simply receive a stored username and password from a password vault.
Therefore, using the same password across multiple applications is not the same as Single Sign-On.
What Is the Relationship Between SSO and IAM?
SSO is an important component of Identity and Access Management (IAM), but SSO is not the same as IAM.
SSO primarily focuses on authentication and simplifying access to applications.
IAM covers a much broader set of responsibilities, including:
- Identity creation
- Authentication
- Authorization
- Access policies
- User provisioning
- Deprovisioning
- Identity governance
- Role management
- Access reviews
- Lifecycle management
A useful way to think about the difference is:
SSO: How does this user authenticate across applications?
IAM: Who is this user, what should they access, and how should that access change throughout their lifecycle?
What Are the Benefits of Single Sign-On?
Better User Experience: Users can access connected applications without repeatedly entering credentials, reducing login friction throughout the workday.
Increased Productivity: Employees spend less time signing into applications and dealing with routine password-related issues.
Reduced Password Fatigue: Users have fewer application-specific passwords to remember, which can reduce password reuse and other poor credential practices.
Centralized Security Controls: IT and security teams can manage authentication policies from a central identity platform. These policies can include MFA, conditional access, session controls, and passwordless authentication.
Fewer Password Reset Requests: Reducing the number of application-specific credentials can reduce some password-related help desk requests.
Improved Visibility and Auditing: Centralizing authentication can provide organizations with greater visibility into authentication activity and application access.
Easier User Lifecycle Management: When SSO is combined with provisioning and deprovisioning capabilities, organizations can simplify access management when employees join, change roles, or leave.
Reduced Shadow IT: Centralized application access can help organizations provide employees with approved applications while maintaining greater visibility and control over access.
Is Single Sign-On Secure?
SSO can improve security, but SSO by itself is not a complete security strategy.
Because authentication is centralized, the identity provider becomes a critical part of the organization's security infrastructure.
If an attacker compromises a user's primary identity account, they may potentially gain access to multiple connected applications.
Organizations should therefore combine SSO with additional security controls such as:
- Multi-factor authentication (MFA)
- Conditional access
- Adaptive authentication
- Device trust
- Endpoint security
- Session controls
- Phishing-resistant authentication
- Passkeys
- Zero Trust security principles
The objective is not simply to make authentication easier. It is to provide strong identity verification and make access decisions according to the organization's security policies.
What Are the Challenges and Risks of SSO?
SSO provides significant benefits, but organizations also need to consider its limitations.
Single Point of Failure: If the identity provider becomes unavailable, users may be unable to authenticate to multiple connected applications.
Compromised Identity Account: A compromised SSO account can potentially affect several applications because the same identity is trusted across multiple services.
Application Compatibility: Not every application supports the same authentication protocols. Legacy applications may require additional integration methods or may not support modern federation standards.
Configuration Complexity: Incorrect configuration of certificates, assertions, claims, redirect URLs, session policies, or access rules can cause authentication failures or security problems.
Certificate Expiration: SAML environments often depend on certificates for signing and validating authentication information. Organizations need processes to monitor certificate expiration and renew certificates before they cause authentication failures.
Session Management: Applications and identity providers may have different session durations and logout behavior. Organizations need to understand how sessions are created, maintained, and revoked.
How Is SSO Implemented?
A successful SSO implementation normally starts with understanding the organization's applications, identity infrastructure, users, and security requirements.
The general process includes:
1. Identify Applications and Users:
Determine which applications need SSO and which groups of users should have access.
2. Select the Identity Provider
Choose an identity platform that fits the organization's existing directory, security requirements, applications, and infrastructure.
3. Select the Authentication Protocol
Determine whether applications will use SAML, OIDC, Kerberos, or another supported authentication mechanism.
4. Establish Trust Between the IdP and SP
Configure identifiers, endpoints, certificates, metadata, redirect URLs, and other required settings.
5. Configure User Attributes and Access
Map attributes such as email, username, department, group, or role where required by the application.
6. Configure Security Policies
Apply MFA, conditional access, device requirements, session policies, and other security controls.
7. Test the Authentication Flow
Test authentication, logout, user attributes, authorization, error handling, certificate validation, and different user scenarios before production deployment.
8. Plan Provisioning and Deprovisioning
Where appropriate, integrate SSO with user lifecycle and provisioning processes so access can be granted and removed as users join, change roles, or leave.
How Does SSO Work With Provisioning and SCIM?
Authentication and user provisioning are related but different processes.
SSO determines how users authenticate.
Provisioning determines how users and their access are created, updated, and removed in applications.
For example, an organization might use SAML or OIDC for SSO while using SCIM (System for Cross-domain Identity Management) to automate user and group provisioning.
This combination can help organizations automate processes such as:
- Creating users
- Updating user attributes
- Assigning groups
- Removing users
- Deprovisioning access
This is particularly useful in larger environments where manually managing accounts across dozens or hundreds of applications becomes difficult.
SSO vs MFA: What Is the Difference?
SSO and MFA solve different problems.
SSO simplifies authentication across multiple applications.
MFA adds additional verification to confirm that the person signing in is actually authorized to use the account.
For example, an organization can require an employee to authenticate through SSO and then use MFA to verify their identity.
Using both together can provide a balance between a simpler user experience and stronger authentication security.
SSO vs Federated Identity: What Is the Difference?
SSO and federated identity are closely related but are not identical.
SSO focuses on allowing users to access multiple applications without repeatedly performing interactive authentication.
Federated identity establishes trust between separate identity domains or organizations so that identity information can be recognized across those environments.
Federated identity can therefore support SSO across organizational boundaries.
How to Choose an SSO Solution
Organizations evaluating an SSO solution should look beyond the number of applications supported.
Important considerations include:
- Application integrations: Does it support your SaaS, custom, legacy, and on-premises applications?
- Protocol support: Does it support SAML, OIDC, OAuth, and other required technologies?
- Security: Does it support MFA, conditional access, device trust, and phishing-resistant authentication?
- Scalability: Can it support your expected growth in users and applications?
- Lifecycle management: Can it support provisioning, deprovisioning, and directory synchronization?
- Administration: Can IT teams easily configure applications and troubleshoot authentication issues?
- Availability: What uptime, resilience, recovery, and operational capabilities does the provider offer?
- Monitoring: Does the platform provide sufficient authentication logs and troubleshooting information?
- API capabilities: Can it integrate with the organization's existing applications and workflows?
The right solution should fit the organization's existing identity architecture while providing enough flexibility to support future applications and security requirements.
What Makes a True SSO System?
A true SSO implementation does more than store or automatically fill usernames and passwords.
The defining characteristic is the trusted authentication relationship between the identity provider and the application.
When a user authenticates through the identity provider, the connected application validates the authentication information provided by that trusted identity system.
This differs from password vaulting, where a system stores credentials and enters them into individual applications.
With SSO, the user's password does not need to be passed from one application to another simply to create the login experience.
What Are the Future Trends in SSO?
SSO continues to evolve alongside broader identity and security technologies.
Several developments are shaping modern SSO environments, including:
- Passwordless authentication
- Passkeys
- Phishing-resistant authentication
- Adaptive authentication
- Risk-based access controls
- Device-based identity
- Automated provisioning and deprovisioning
- Stronger integration between SSO and IAM
- Zero Trust security models
As organizations adopt more cloud applications and distributed work environments, centralized identity and access management will remain an important part of enterprise security.
Conclusion
Single Sign-On (SSO) allows users to access multiple trusted applications through centralized authentication rather than maintaining separate login credentials for every application.
SSO commonly works through an Identity Provider and Service Provider relationship, with technologies such as SAML, OpenID Connect, OAuth 2.0, and Kerberos supporting different authentication and authorization requirements.
While SSO can improve user experience, productivity, security management, and access visibility, it should be implemented alongside controls such as MFA, conditional access, lifecycle management, and appropriate identity governance.
For organizations evaluating an SSO implementation, the right approach depends on the applications, users, identity infrastructure, security requirements, and authentication protocols already in use.
If you're evaluating SSO for your organization, explore Integer Cloud's SSO solution to understand how centralized authentication can support your application environment.
Frequently Asked Questions About Single Sign-On
What does SSO stand for?
SSO stands for Single Sign-On. It is an authentication method that allows users to access multiple trusted applications after authenticating through an identity provider.
What happens to active user sessions when an employee leaves an organization?
The exact behavior depends on the identity provider, application, session duration, and deprovisioning setup. Removing or disabling the user's identity can prevent future authentication, while existing application sessions may require separate session-revocation controls.
What is an Identity Provider in SSO?
An Identity Provider (IdP) is a system that authenticates users and provides trusted identity information to applications.
What is a Service Provider in SSO?
A Service Provider (SP) is the application or service that a user wants to access. It relies on the identity provider to authenticate the user.
Is SSO the same as a password manager?
No. A password manager stores credentials and can automatically fill them into individual applications. SSO establishes a trusted authentication relationship between the identity provider and connected applications.
Is SSO secure?
SSO can improve security when properly implemented, but it should be combined with controls such as MFA, conditional access, device security, session management, and phishing-resistant authentication.
What protocols are used for SSO?
Common technologies include SAML, OpenID Connect, OAuth 2.0, and Kerberos. SAML and OIDC are particularly important for application authentication, while OAuth 2.0 is primarily an authorization framework.
What is the difference between SSO and MFA?
SSO reduces repeated authentication across applications, while MFA requires users to provide additional verification factors. Organizations commonly use both together.
Can Single Sign-On support third-party partners, vendors, or contractors?
Yes. Federated identity can allow external users to access applications without creating separate credentials for every system. The organization still needs appropriate policies around guest identities, access scope, lifecycle management, and offboarding.
Can SSO work with cloud and on-premises applications?
Yes. SSO can support both cloud and on-premises applications, provided the applications and identity infrastructure support compatible authentication or integration methods.
What is SCIM's role in SSO?
SCIM is primarily used for automated identity provisioning and deprovisioning. It complements SSO by helping organizations create, update, and remove user accounts across connected applications.
What happens if the SSO provider goes down?
If the identity provider becomes unavailable, users may be unable to authenticate to applications that depend on it. Organizations should therefore consider availability, resilience, recovery, and appropriate emergency access procedures when designing an SSO environment.
How do you measure the success of an SSO implementation?
Organizations can measure SSO using metrics such as application adoption, authentication failure rates, password-reset volume, login-related help desk requests, application coverage, onboarding and offboarding time, MFA adoption, and security-policy compliance.