I Studied How Google Signs You Into All Services With One Login. Here's What I Learned

At Hexmos, we have few products—LiveAPI, Feedzap, Feedback, and more to come. Previously, each product required users to sign in separately, which created friction for users to try out other products.

We wanted to solve this by implementing a Single Sign-On (SSO) system. Inspired by Google’s seamless login process, I studied their system, analyzed their login flow, and explored the technical foundations that make it work. Here’s what I learned and how these insights shaped our approach.

Decoding the Magic Behind Google's One-Click Login

Google’s login system is often regarded as the gold standard for seamless authentication. Users can access a wide range of services like Gmail, Drive, and YouTube with a single click, without repeatedly entering credentials. But how does this work behind the scenes?

At its core, Google’s SSO system relies on a combination of Identity Providers (IdPs), Service Providers (SPs), cookies, tokens, and robust protocols to manage authentication across domains and services. By examining their approach, we can understand the building blocks of an effective SSO implementation.

Google's Identity Arsenal: Identity Providers and Service Providers

In the SSO ecosystem, Google exemplifies the interaction between Identity Providers (IdPs) and Service Providers (SPs) to enable seamless user experiences:

• Identity Providers (IdPs): IdPs authenticate users and issue tokens or credentials verifying their identity. Google’s IdP, for example, allows users to log in once and access services like Gmail, YouTube, or Google Drive.

• Service Providers (SPs):  SPs consume the authentication the IdP provides. When a user logs in to accounts.google.com (the IdP), other services like Google Docs or Calendar (SPs) trust the credentials issued by the IdP and allow access without a second login.

This relationship ensures secure, unified access management while eliminating redundant authentication, streamlining both user experience and security processes.

Analising Google's Login Flow By Seeing Network Requests

1. First Time Signing in
   I am Trying to access Google Meet
   

This page Will Open in same tab
URL:
https://accounts.google.com/...&checkConnection=youtube%3A613&checkedDomains=youtube&...&continue=https%3A%2F%2Fmeet.google.com%3Fhs%3D193&...

I observed the following network requests:

• checkConnection and checkedDomains query parameters:
  &checkConnection=youtube%3A613&checkedDomains=youtube
  Indicates that the login process might connect to YouTube as well.

• Post-login redirect:
  &continue=https%3A%2F%2Fmeet.google.com%3Fhs%3D193
  After signing in, the user will be redirected to Google Meet at https://meet.google.com?hs=193.

After Signing in

Description: This image shows the page displayed after redirection from the login page.

The Role of Cookies and Tokens

Cookies and tokens are vital mechanisms for maintaining authenticated sessions:

• Cookies: Primarily used in browser-based applications, cookies store user session data on the client side. Session cookies allow persistent user states across pages within the same domain. However, third-party cookies face increasing restrictions due to privacy concerns.
• Tokens: Token-based authentication (e.g., JWTs) enables secure communication between the client and server. Tokens are portable, can work across domains, and are typically used in modern SSO systems where browsers block third-party cookies.

Both methods establish trust, but tokens provide better scalability and cross-domain compatibility, making them ideal for SSO implementations.

Exploring Cookie Behavior During Login and Logout

Before Logging In

This image shows the state of the cookies before logging in. Notice that no user-related cookies have been set yet.

After Logging In

This image highlights the cookies after logging in, showing the user-specific data added during the login process.

YouTube Before Login

Cookies for YouTube before logging in indicate no session or personalized data is yet stored.

YouTube Cookies Also Updated

Upon logging in, YouTube cookies are also updated, reflecting login session data synchronized across Google services.

YouTube on Logout

This image illustrates the state of YouTube cookies after logout, showing the removal of user-specific session data.

Important Feature: Clear Cookies on Logout

When logging out, an API call ensures that cookies are cleared to protect user session data.

Clear Cookies API

https://accounts.youtube.com/accounts/ClearSID?zx=-1418421220&continue=https://www.youtube.com/&ccSIDsig=APPch3ND4-fYte7MDDxknZ53JKIH
This API is responsible for clearing cookies. It ensures no sensitive session data remains after logout.

Before Clearing Cookies

The image above shows the state of cookies before they are cleared, still containing session-related information.

API in Action: Clearing Cookies

The image above demonstrates the API being invoked to clear the cookies.

After Clearing Cookies

This image shows the state of cookies after they are cleared, ensuring that no session data remains.

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Same-Domain vs. Cross-Domain SSO

Same-Domain SSO

• In a single domain, SSO is simpler. The IdP can leverage session cookies to maintain user authentication state across multiple services hosted on the same domain (e.g., mail.google.com and meet.google.com).
• Session cookies are tied to the root domain, allowing frictionless transitions without re-authentication.

Cross-Domain SSO

• Challenges: Cross-domain SSO involves authentication across entirely different domains (e.g., google.com and youtube.com). Challenges include browser restrictions on third-party cookies, token sharing, and potential security vulnerabilities.
• Solutions:
  • Token-Based Authentication: Modern systems use JWTs or similar tokens to securely transmit user authentication states between domains.
  • Cloudflare Workers: Edge-based solutions like Cloudflare Workers (or OpenFaaS) enable authentication by redirecting traffic and securely validating requests. This approach bypasses browser limitations and supports global scaling.

Comparison Table:

The Power of SSO: Benefits for Users and Businesses

SSO benefits both users and businesses significantly:

For Users

• Convenience: One login unlocks access to multiple services.
• Time-Saving: Reduced time spent entering credentials.
• Enhanced Security: Fewer credentials to manage and reduce the likelihood of weak or reused passwords.

For Businesses

• Increased Productivity: Employees spend less time dealing with login issues.
• Improved User Retention: Simplified logins encourage users to stay engaged with multiple services.
• Cost Savings: Reimplementing login and password reset functionality in every product can be avoided, reducing development effort and IT overhead.

Implementing SSO in Your Product

Choose an Authentication Protocol

• SAML (Security Assertion Markup Language): Best for enterprise environments; uses XML-based assertions for authentication.
• OAuth 2.0: A flexible, widely-used protocol for authorization. Suitable for consumer-facing applications.
• OpenID Connect (OIDC): Built on OAuth 2.0; simplifies user identity management with JSON Web Tokens (JWTs).

Integrate with an Identity Provider

• Cloud-Based IdPs: Platforms like Google, Okta, or Auth0 simplify setup and scalability.
• Self-Hosted IdPs: Building your own IdP allows greater control but requires more resources. Configuration involves defining trust relationships, setting up metadata exchanges, and ensuring encryption for token transmission.

Configure Service Providers

• Trust Relationships: SPs must trust tokens issued by the IdP to authenticate users.
• Session Management: Implement single logout (SLO) to invalidate user sessions across all services when they log out of one.

Conclusion

The Future of SSO

As privacy regulations and browser policies evolve, SSO will increasingly rely on token-based systems, edge computing solutions, and decentralized authentication mechanisms like blockchain.

Implementing SSO in Your Application

Adopting SSO requires careful planning and execution, from selecting the right protocol to integrating with IdPs and SPs. By implementing SSO effectively, you can enhance security, simplify user experiences, and future-proof your application for scalable growth.

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