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What is CORS? CORS (Cross-Origin Resource Sharing) is a browser security mechanism that controls which websites can make API calls to other domains. What is an Origin? Origin = Protocol + Domain + Port https://example.com:443 ↑ ↑ ↑ Protocol Domain Port Same-Origin Examples: Origin 1: https://example.com/page1 Origin 2: https://example.com/page2 → Same origin ✓ Cross-Origin Examples: Origin 1: https://example.com Origin 2: https://api.example.com → Different domain = Cross-origin ✗ Origin 1: https://example.com Origin 2: http://example.com → Different protocol = Cross-origin ✗ Origin 1: https://example.com:443 Origin 2: https://example.com:8080 → Different port = Cross-origin ✗ Why CORS Exists Without CORS: ...

What is Corporate Proxy with SSL Inspection? Corporate proxies intercept HTTPS traffic to inspect content for security and compliance. This is called SSL Inspection or MITM (Man-In-The-Middle). Complete Flow: curl Through Proxy Command: curl -v -x http://proxy.company.com:8080 https://api.example.com/data Step-by-Step Flow: 1. DNS Resolution curl resolves proxy hostname ↓ DNS: proxy.company.com → 192.168.1.100 2. TCP Connection to Proxy curl → proxy:8080 ↓ TCP handshake: SYN, SYN-ACK, ACK ↓ Connection established 3. CONNECT Request (HTTP Tunnel) curl sends: → CONNECT api.example.com:443 HTTP/1.1 → Host: api.example.com → User-Agent: curl/8.0.0 → Proxy-Connection: Keep-Alive Proxy responds: ← HTTP/1.1 200 Connection established Key point: CONNECT doesn’t create new TCP connection - it repurposes existing connection as tunnel. ...

What is HAR File? HAR (HTTP Archive) is a JSON format for recording browser HTTP transactions. Created by exporting from Browser DevTools Network tab. How to Create HAR File Chrome/Edge: 1. F12 → Network tab 2. Reload page or perform action 3. Right-click any request 4. "Save all as HAR with content" Firefox: 1. F12 → Network tab 2. Click gear icon → "Save All As HAR" HAR File Structure Overview { "log": { "version": "1.2", "creator": { ... }, "browser": { ... }, "pages": [ ... ], "entries": [ ... ] } } Complete HAR Structure Root Object { "log": { "version": "1.2", "creator": { "name": "WebInspector", "version": "537.36", "comment": "" }, "browser": { "name": "Chrome", "version": "142.0.0.0", "comment": "" }, "pages": [ { "startedDateTime": "2025-11-28T10:30:45.123Z", "id": "page_1", "title": "Example Page", "pageTimings": { "onContentLoad": 1234.5, "onLoad": 2345.6 } } ], "entries": [ { "pageref": "page_1", "startedDateTime": "2025-11-28T10:30:45.123Z", "time": 308.5, "request": { ... }, "response": { ... }, "cache": { ... }, "timings": { ... }, "serverIPAddress": "192.168.1.100", "connection": "443", "_initiator": { ... }, "_priority": "High", "_resourceType": "fetch" } ] } } log Object Top-level container for all HAR data. ...