Solution: Authenticate Users with Configurable Login and Tokens

Explore how to apply the Strategy Pattern to build a flexible authentication system in Node.js. Learn to implement multiple login methods like password, OTP, and Google along with different token generation strategies. Understand how to compose these strategies in a controller to handle authentication and token issuance seamlessly without conditional logic.

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Solution explanation
Revisit the problem statement

Solution explanation

Lines 2–27: Define three authentication strategies: PasswordAuth, OtpAuth, and GoogleAuth.
- Each has an async .authenticate() that simulates real checks with setTimeout().
- PasswordAuth checks a simple password string.
- OtpAuth verifies a fixed OTP code.
- GoogleAuth validates a token prefix.
- All follow a shared interface, so the context can delegate uniformly.
Lines 30–54: The AuthService and TokenService are independent contexts.
- Each stores its active strategy and delegates calls to it.
- Both can switch strategies at runtime using .setStrategy().
- There are no conditionals—the behavior is entirely determined by which strategy is active.
Lines 57–81: The token strategies—SessionToken ...

1.Introduction to Node.js Patterns

2.Factory Pattern: Generate Config-Driven Services Dynamically

3.Builder Pattern: Assemble Complex Objects with Fluent APIs

4.Decorator Pattern: Extend Behavior Without Modifying Core Logic

5.Adapter Pattern: Standardize Interface Across Dependencies

6.Proxy Pattern: Intercept and Control Access Transparently

7.Strategy Pattern: Swap Algorithms Based on Context

8.Wrapping Up

Solution: Authenticate Users with Configurable Login and Tokens

Solution explanation