Single Sign-On Implementation: Complete Technical Guide

01What is Single Sign-On?

Single Sign-On (SSO) allows users to authenticate once and access multiple applications without re-entering credentials. It improves user experience while enhancing security through centralized authentication.

02SSO Protocols Explained

SAML 2.0 (Security Assertion Markup Language)

Best For: Enterprise applications, legacy systems

How It Works:

1. User attempts to access Service Provider (SP)
2. SP redirects to Identity Provider (IdP)
3. IdP authenticates user
4. IdP sends SAML assertion to SP
5. SP grants access based on assertion

Key Components:

• Assertion: XML document with authentication/authorization data
• Metadata: Configuration exchange between IdP and SP
• Bindings: How messages are transported (HTTP-POST, HTTP-Redirect)

OAuth 2.0 / OpenID Connect

Best For: Modern applications, APIs, mobile apps

How It Works (Authorization Code Flow):

1. User clicks login, redirected to IdP
2. User authenticates at IdP
3. IdP returns authorization code
4. Application exchanges code for tokens
5. Application uses access token for APIs

Key Components:

• ID Token: JWT containing user identity claims
• Access Token: Token for API authorization
• Refresh Token: Token for obtaining new access tokens

Protocol Comparison

03Technical Architecture

Components

``` ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ │ User │────▶│ Browser │────▶│ Application │ └─────────────┘ └─────────────┘ └──────┬──────┘ │ ▼ ┌─────────────┐ │ IdP │ │ (Okta/ │ │ Entra ID) │ └─────────────┘ ```

IdP-Initiated vs SP-Initiated SSO

SP-Initiated (Recommended):

1. User visits application first
2. Application redirects to IdP
3. After auth, IdP redirects back

IdP-Initiated:

1. User starts at IdP portal
2. Clicks application tile
3. IdP sends assertion to SP

04Implementation Steps

Step 1: Choose Your Protocol

Use SAML 2.0 when:

• Integrating with enterprise applications
• Application only supports SAML
• Need attribute-based access control

Use OIDC when:

• Building modern web/mobile apps
• Need API access
• Want simpler implementation

Step 2: Configure Identity Provider

For Okta:

1. Create new application integration
2. Select SAML 2.0 or OIDC
3. Configure SSO URL and entity ID
4. Set attribute mappings
5. Download metadata/credentials

For Microsoft Entra ID:

1. Go to Enterprise Applications
2. Create new application
3. Configure SSO settings
4. Set up user provisioning
5. Assign users/groups

Step 3: Configure Service Provider

SAML SP Configuration:

```xml

\`\`\`

OIDC Client Configuration:

```javascript // OIDC Configuration const config = { client_id: 'your-client-id', redirect_uri: 'https://app.example.com/callback', response_type: 'code', scope: 'openid profile email', authority: 'https://your-idp.com' }; ```

Step 4: Implement Authentication Flow

OIDC Implementation Example (JavaScript):

```javascript // Redirect to login function login() { const authUrl = `${config.authority}/authorize? client_id=${config.client_id}& redirect_uri=${config.redirect_uri}& response_type=code& scope=${config.scope}& state=${generateState()}`;

window.location.href = authUrl; }

// Handle callback async function handleCallback() { const code = getUrlParam('code');

const tokenResponse = await fetch(`${config.authority}/token\