CORS Error Despite Headers Present (Preflight OPTIONS Request Failing)
When your actual API endpoint clearly returns correct CORS headers, but the browser still blocks the request with a CORS error, the real problem is almost...
Category
Cybersecurity / Networking
Practical fixes for authentication errors, API security issues, and network debugging basics.
CSRF Token Missing or Incorrect in SPA Frontend Requests
CSRF token errors in an SPA almost always come down to the frontend not correctly obtaining the current token before making a request, or not attaching it in...
OAuth 2.0 "invalid_grant" Redirect URI Mismatch Fix
An invalid_grant error during an OAuth token exchange very often means the redirect_uri sent in the token request doesn't exactly match the one used in the...
Rate Limit 429 Too Many Requests Bypass During Load Testing
Getting rate-limited while load testing your own API is expected behavior — the rate limiter is doing its job — and the correct fix is configuring a...
SSL Certificate Chain Incomplete Error on API Clients
When an SSL certificate works fine in a browser but fails specifically for API clients, command-line tools, or certain programming language HTTP libraries, it...
API Key Exposed in Frontend Code, How to Fix
An API key exposed in frontend code is a genuine security incident, not just a code smell — anything shipped to the browser is visible to anyone who opens...
HTTPS Mixed Content Warning, How to Resolve
A mixed content warning means a page served over HTTPS is loading at least one resource (an image, script, stylesheet, or API call) over plain HTTP — browsers...
Rate Limiting an API Correctly, Common Mistakes
Rate limiting looks simple on the surface — count requests, block when a threshold is exceeded — but several common implementation mistakes either leave the...
Session Hijacking, Practical Prevention Basics
Session hijacking means an attacker obtains a valid session identifier belonging to another user and uses it to impersonate them, without needing to know their...