JWT "Invalid Signature" Error When Validating Token Across Microservices
A JWT that validates fine within the service that issued it, but fails with "invalid signature" when validated by a different microservice, means the two...
Category
Cybersecurity / Networking
Practical fixes for authentication errors, API security issues, and network debugging basics.
Rate Limiting Bypass via X-Forwarded-For Header Spoofing, How to Block It
If your rate limiter keys off the X-Forwarded-For header without validating where that header actually came from, an attacker can trivially bypass rate...
SSL Certificate Expired Error on curl Command Despite Browser Working
When curl reports an expired certificate but every browser connects to the same site without any warning, the certificate itself almost certainly isn't...
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...
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...