How google handle sso

Google uses a secure SSO mechanism to manage authentication across its services (like Gmail, YouTube, and Google Drive). While it might seem like Google is using iframes for verifying the user's connection between services, the actual process is more sophisticated, and iframes are not the primary method for handling authentication.

Here’s a breakdown of how Google likely handles SSO:

1. Single Sign-On Architecture:

Google uses a combination of OAuth 2.0 and OpenID Connect to manage authentication across its services. The core idea is that once a user is authenticated on any Google service, they remain logged in across all other Google services that rely on the same central authentication system (Google's Identity Provider).

2. How Google SSO Works:

• Central Authentication Server: Google has a central identity provider (IDP) that manages all login sessions.

• OAuth 2.0 / OpenID Connect: When a user signs in to Google, they authenticate using OAuth 2.0 and OpenID Connect, which issues tokens (access tokens, ID tokens) to allow other Google services (like YouTube) to verify the user.

• Session Cookies: After logging in, Google sets a session cookie for the entire Google domain (e.g., *.google.com). This cookie is shared across all Google services.

When a user navigates to a service like YouTube, the app checks the session cookie from google.com to see if the user is authenticated. If the cookie is valid, the user is automatically signed in to YouTube without needing to log in again.

3. Token Verification via iframe or CORS (Cross-Origin Requests):

Sometimes it may appear that Google is using iframes to verify a user’s login status on services like YouTube, but it’s more likely that Google uses Cross-Origin Resource Sharing (CORS) or third-party cookies to check if a user is logged in.

• CORS: When you visit YouTube, the site might make a request to the Google SSO endpoint (accounts.google.com) to verify if you're logged in. If so, the service can retrieve the appropriate token and log you in automatically.

• iframes (for re-authentication): While Google generally avoids iframes for full authentication, it may occasionally use them to silently check a user's session status without interrupting the main page experience. This is often combined with postMessage API to securely pass tokens between the iframe and the main window.

  For example, a YouTube page might embed an invisible iframe pointing to a Google SSO URL to check if the user is authenticated. If the iframe detects a valid session, it can securely pass that information back to YouTube.

How You Can Set Up a Similar SSO Mechanism:

1. Use OAuth 2.0 and OpenID Connect: Set up your own SSO system using OAuth 2.0 for authorization and OpenID Connect for authentication. Most SSO providers and identity management platforms, like Auth0, AWS Cognito, or Keycloak, offer built-in support for these protocols.

2. Centralized Identity Provider (IDP): Create or use an existing centralized identity provider to manage user sessions across multiple applications. The IDP issues a token (ID token, access token) after a user logs in, which can be used across your applications.

3. Session Management and Tokens:

   • Once a user logs in, set a session cookie or store tokens (such as JWTs) to verify their authentication across services.

   • Tokens (like JWTs) can be shared securely between applications using Cross-Origin Resource Sharing (CORS), redirects, or iframes with postMessage (if needed).

4. Silent Authentication (Optional):

   • You can use invisible iframes or make CORS requests to the central authentication server to silently check if the user is logged in.

   • The silent authentication will return a valid session/token if the user is authenticated, allowing the application to log them in without explicit interaction.

Steps to Implement OAuth/OpenID Connect:

1. Create an Identity Provider (IDP): Use platforms like Keycloak, Auth0, or AWS Cognito to handle user authentication, or create your own with OAuth 2.0.

2. SSO Flow:

   • Redirect the user to the central identity provider (IDP) for login.

   • After login, the IDP will issue a token (JWT or similar) and redirect the user back to the original service.

   • Each service can verify the token with the IDP to ensure the user is authenticated.

3. Handling Multiple Services:

   • When a user visits a new service (e.g., YouTube after Gmail), the service will automatically check for the authentication token (e.g., via cookies or a silent iframe).

   • If the token is valid, the service logs the user in without requiring credentials again.