Intermediate LevelREST APIs & Web Services
How does the OAuth 2.0 Authorization Code Grant Flow with PKCE operate?
❓ Interview Prompt: Explain OAuth 2.0 PKCE (Proof Key for Code Exchange), Code Verifier, Code Challenge, Authorization Code, Access Token, and securing public SPA/mobile apps.
OAuth 2.0 Authorization Code Flow with PKCE (RFC 7636) is the gold standard authentication framework for single-page apps (SPAs) and mobile devices:
PKCE Security Mechanics:
1
Code Verifier: Client generates a cryptographically random secret string.
2
Code Challenge: Client creates a SHA-256 hash of the verifier ('BASE64URL(SHA256(verifier))').
3
Auth Code Request: Client redirects user to authorization server passing 'code_challenge'.
4
Token Exchange: Client exchanges auth code for JWT tokens by passing the original 'code_verifier' secret. The server hashes it and verifies match, preventing authorization code interception attacks!
Code Implementation Example
typescript
import crypto from 'crypto';
// Generate PKCE Code Verifier & Code Challenge
const codeVerifier = crypto.randomBytes(32).toString('base64url');
const codeChallenge = crypto
.createHash('sha256')
.update(codeVerifier)
.digest('base64url');
console.log({ codeVerifier, codeChallenge });💡Generating OAuth 2.0 PKCE code verifier and challenge strings in TypeScript.
🎯 Interview Key Takeaway
Use OAuth 2.0 Authorization Code Flow with PKCE to secure public SPA and mobile API clients against token interception.
#OAuth 2.0#PKCE#Security#Tokens#Intermediate
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