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Single Sign-On (SSO)

A comprehensive guide to SSO and authentication protocols

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Overview

Single Sign-On (SSO) enables users to access multiple systems with a single authentication process.

What is SSO?

SSO is an authentication scheme that allows users to access multiple applications with one set of credentials. It:

  • Improves user experience
  • Reduces authentication complexity
  • Enhances security
  • Centralizes access management

Key Benefits

1. Enhanced User Experience
   - Single login for multiple services
   - Reduced password management

2. Improved Security
   - Centralized authentication
   - Stronger password policies

3. Efficient Resource Management
   - Centralized user management
   - Simplified administration


Authentication Protocols

OAuth (Open Authorization)

Purpose:
- Delegation of access rights
- Third-party application authentication
- API authorization

Operation:
- Token-based authentication
- Resource owner authorization
- Defined access scopes
sequenceDiagram participant User as User participant ClientApp as Client Application participant AuthServer as Authorization Server participant ResourceServer as Resource Server User->>ClientApp: Request access to resource ClientApp->>AuthServer: Redirect user for authentication AuthServer->>User: Authenticate and grant permission AuthServer-->>ClientApp: Return authorization code ClientApp->>AuthServer: Exchange auth code for access token AuthServer-->>ClientApp: Access token ClientApp->>ResourceServer: Request resource with access token ResourceServer-->>ClientApp: Return resource


SAML (Security Assertion Markup Language)

Purpose:
- Enterprise SSO
- XML-based framework
- Identity provider communication

Operation:
- IdP authentication
- SAML assertions
- Service provider validation
sequenceDiagram participant User as User participant ServiceProvider as Service Provider participant IdentityProvider as Identity Provider User->>ServiceProvider: Access request ServiceProvider->>User: Redirect to IdP for SSO User->>IdentityProvider: Authenticate (if not already) IdentityProvider-->>ServiceProvider: SAML Assertion (authentication response) ServiceProvider->>IdentityProvider: SAML Assertion ServiceProvider-->>ServiceProvider: Validate Assertion and create session ServiceProvider-->>User: Access granted


OIDC (OpenID Connect)

Purpose:
- Identity layer over OAuth 2.0
- User authentication
- Profile information access

Operation:
- JWT-based ID tokens
- OAuth 2.0 extension
- RESTful implementation
sequenceDiagram participant User as User participant ClientApp as Client Application participant OpenIDProvider as OpenID Provider User->>ClientApp: Request login ClientApp->>OpenIDProvider: Redirect user to OP OpenIDProvider->>OpenIDProvider: Authenticate OpenIDProvider->>User: Consent (if required) OpenIDProvider-->>ClientApp: ID Token + 🔑 Access Token ClientApp->>ClientApp: Validate ID Token ClientApp-->>User: User logged in


📊 OAuth vs SAML vs OIDC Comparison

Feature OAuth SAML OIDC
Primary Use Authorization Enterprise SSO Authentication
Format JSON/JWT XML JSON/JWT
Complexity Medium High Low
Modern Apps Yes Limited Yes
Mobile Support Good Limited Excellent


Reference