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

At Hexmos, we have few products—[LiveAPI](https://hexmos.com/liveapi), [Feedzap](https://hexmos.com/feedzap#tab-ForMe), [Feedback](https://hexmos.com/feedback), and more to come. Previously, each product required users to sign in separately, which creates a friction for the user 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:

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- **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.

**First Time Signing in**

`https://accounts.google.com/v3/signin/challenge/pwd?TL=AKOx4s17KNL__c4dOeSmdyfXWMR99LUWaAdBtcAjcPk64YtZ6rJtNgVhC60K3ZG-&checkConnection=youtube%3A613&checkedDomains=youtube&cid=2&continue=https%3A%2F%2Fmeet.google.com%3Fhs%3D193&ddm=1&dsh=S473575397%3A1732374296736218&ec=wgc-meet-globalnav-signin&flowEntry=ServiceLogin&flowName=GlifWebSignIn&ifkv=AcMMx-dz7cjwqHMTVaRYOL1G5I5xMLZTLIvH-GY5RAM1yWlxG1J_e2MuNgHZSWI9ngU1vDKmM2ecBw&ltmpl=meet&pstMsg=1`


**After Siging in**

- **Service Providers (SPs):** SPs consume the authentication provided by the IdP. 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.

When I open `meet.google.com`

`https://accounts.google.com/ServiceLogin?ltmpl=meet&continue=https://meet.google.com?hs=193&ec=wgc-meet-globalnav-signin`



https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/302

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

### **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.
**Before Logging In**
**After Logging In**

**Youtube Befor Login **

**Youtube Cookies Also Updated**

**Youtube on Logout**

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

**Clear Cookies**

`https://accounts.youtube.com/accounts/ClearSID?zx=-1418421220&continue=https://www.youtube.com/&ccSIDsig=APPch3ND4-fYte7MDDxknZ53JKIH`

It will Clear all Cookies

Afer Clearing Cookies

### **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., `example.com` and `another-example.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.

### Will change image in a while


**Comparison Table**:

|Requirement|Use Cookies|Use Cloudflare Workers([Openfaas](https://www.openfaas.com/))|
|---|---|---|
|Same root domain|✅|❌|
|Different root domains|❌|✅|
|Need for global scaling|❌|✅|
|Browsers blocking third-party cookies|❌|✅|
|Minimal latency|✅|❌ (due to redirection overhead)|


### **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 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:** Fewer password reset requests and simpler access management reduce 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 Own 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.

External Sources

https://www.reddit.com/r/howdidtheycodeit/comments/xxc74h/how_does_signing_into_google_automatically_sign/

https://www.quora.com/How-does-Google-achieve-single-sign-on-between-different-domains-such-as-YouTube-and-Gmail