Client

A fast-growing SaaS platform offering multi-user access across web and mobile apps. As their user base grew, their old login system couldn’t handle the load and lacked security controls.

They needed:

• Secure login

• Scalable token management

• Role-based access control

• Support for multiple user types

• OAuth2 compatibility

• Zero downtime authentication flow

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Project Overview

We built a modern, scalable, cloud-ready authentication and authorization system that supports:

• JWT-based stateless authentication

• OAuth2 provider integration

• Session-based fallback (optional)

• RBAC (Role-Based Access Control)

• Secure refresh token lifecycle

• User/device-level access rules

Designed to handle millions of tokens and thousands of concurrent logins.

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Key Challenges

1. Legacy Auth System

The old system used simple sessions with no refresh tokens and limited security.

2. Multi-Tenant Requirements

Different departments and user types required different access levels.

3. Scalability

Auth system had to handle:

• Peak login spikes

• Mobile apps refreshing tokens

• API gateways validating millions of requests

4. Security

Protection needed against:

• Token theft

• Session hijacking

• CSRF

• Bruteforce attacks

• Improper authorization checks

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Our Solution

1. Implementing JWT-Based Authentication

JWT was chosen for:

• Stateless validation

• No server-side session storage

• Fast API gateway validation

We used:

• Access Tokens (short-lived)

• Refresh Tokens (long-lived) stored securely

• Rotating tokens to prevent replay attacks

• Device-wise token tracking

Security Features:

• HS256/RS256 signing

• Token blacklist for compromised tokens

• Strict expiry and refresh logic

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2. OAuth2 Integration for Third-Party Access

We enabled OAuth2 flows:

• Authorization Code Flow (web)

• PKCE (mobile)

• Client Credentials Flow (server-to-server)

Supported providers:

• Google

• Microsoft

• GitHub

• Enterprise SSO (via OpenID Connect)

This enabled:

• Quick onboarding

• Single sign-on (SSO)

• Secure federated login

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3. Optional Session-Based Authentication

For internal admin apps, we provided session-based auth:

• Secure cookies

• SameSite + HTTPOnly flags

• Server-side session store (Redis for performance)

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4. Role-Based Access Control (RBAC)

We implemented a flexible RBAC system:

Entities:

• Roles (Admin, Manager, Staff, Customer, API Client)

• Permissions (read, write, delete, approve, upload)

• Resources/Modules

Dynamic:

• Roles can be assigned dynamically

• Permissions checked at request-time

• Fine-grained access rules

All validation happens via:

• Middleware interceptors

• API gateway policies

• Attribute-based checks (optional)

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5. Central Authentication Server (Auth Service)

We built a dedicated microservice for authentication:

• Sign-in / Sign-up

• Refresh tokens

• Password reset

• OAuth2 callback handling

• JWT issuance/validation

This ensured clean separation and easy scaling.

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6. Hardening & Security Controls

Included:

• Password hashing (Argon2 / bcrypt)

• Rate limiting for login endpoints

• MFA/Two-Factor Authentication (optional)

• IP/device-based restrictions

• Audit logs of auth events

• Email + mobile verification

• Brute-force detection

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7. API Gateway Integration

To secure downstream microservices:

• Token validation at gateway

• RBAC validation at gateway or service layer

• Central logging & observability

This reduced load on backend microservices.

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Architecture Diagram (Text Version)

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Results & Impact

🟢 Zero Downtime Auth

New system deployed without breaking sessions or tokens.

🔒 Strong Security

256-bit JWT signing, MFA, RBAC — all in place.

💨 Fast Token Validation

Stateless JWT validation improved request latency significantly.

📈 Scalable Authentication

Handles:

• Millions of tokens

• 1000s of concurrent logins

• Mobile + Web traffic

👥 Secure Multi-User Environment

Fine-grained RBAC ensures every user sees only what they’re allowed to.

🔁 Reduced Auth-Related Errors

Clear flows + better token lifecycle = fewer support tickets.

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Conclusion

By designing a scalable authentication and authorization system with JWT, OAuth2, and RBAC, we gave the client a future-proof security foundation.

The system is now:

• Robust

• Scalable

• Secure

• Easy to extend

• Suitable for multi-tenant platforms

A strong backbone for user identity, access control, and API protection.