Caddy makes the easy path easy, but CORS is still CORS. The browser enforces it, the server has to answer correctly, and one wrong header can turn a simple API call into a weird frontend bug that eats an afternoon. This guide is the version I wish I had the first few times I configured CORS behind a reverse proxy. What CORS is actually doing CORS is the browser asking: ...
CORS on Vultr is usually not a Vultr problem. It’s an app server, reverse proxy, or object storage config problem that just happens to show up on a Vultr VM, Kubernetes cluster, or load balancer. I’ve seen teams lose hours blaming firewalls, DNS, even TLS, when the real bug was one missing OPTIONS response or a wildcard used with credentials. So here’s the practical version: what to set, where to set it, and what not to do. ...
CORS in a Flutter WebView trips people up because there are really two different worlds hiding behind one app: Flutter web, where your app runs in a browser and CORS rules fully apply. Flutter mobile with a WebView, where browser-like behavior exists, but native networking and embedded browser behavior can change the story. If you treat a WebView like “just Chrome inside Flutter,” you’ll misdiagnose bugs for hours. I’ve done that. The fix usually starts with one question: ...
CORS and API versioning tend to collide in ugly ways once an API leaves the whiteboard and hits browsers, CDNs, mobile clients, and a few years of “temporary” backwards compatibility. I’ve seen teams treat them as separate concerns: versioning is for API design, CORS is for frontend access. That split works right up until you ship v2, your browser app starts sending different headers, preflights spike, and suddenly half your cross-origin traffic is failing for reasons no one can reproduce with curl. ...
A lot of CORS bugs don’t start in the app. They start at the edge. I’ve seen teams spend days debugging “random” frontend failures only to find the real issue sitting in a CDN rule added six months earlier by someone trying to improve cache hit ratio. The app was fine. The browser was fine. The CDN was serving the wrong CORS headers to the wrong origin. That’s the messy reality of global CDN configurations: once responses are cached and reused across regions, CORS mistakes get amplified fast. ...
A few years ago I helped untangle a Drupal setup that looked fine in local dev and completely fell apart in production. The stack was common enough: Drupal serving JSON:API a separate frontend on another origin authenticated requests for logged-in users some custom headers from the frontend a CDN and reverse proxy in front of Drupal Everybody thought “CORS is enabled” meant the problem was solved. It wasn’t. The symptoms were classic: ...
CORS on Azure Functions looks simple until you ship something with auth, multiple environments, and a frontend team that keeps changing origins every sprint. I’ve seen teams treat CORS as a checkbox in the Azure Portal, then spend hours debugging why Authorization headers fail, why local dev works but production doesn’t, or why preflight requests get blocked before their function code even runs. If you’re building browser-facing APIs on Azure Functions, you have a few ways to handle CORS. Some are easy. Some are flexible. Some are traps. ...
CORS and CSRF get lumped together way too often. I’ve seen teams say “we enabled CORS, so we’re protected from CSRF now” and then act surprised when their app still has a cross-site request forgery bug. That’s the core mistake: these are not competing solutions to the same problem. They deal with different threats, at different layers, using different browser behavior. If you only remember one thing, make it this: ...
If you build a Rails API and your frontend runs on a different origin, CORS stops being theory pretty fast. You ship an endpoint, the browser blocks it, and suddenly everyone is staring at a console error that says “No ‘Access-Control-Allow-Origin’ header.” Rails itself does not magically solve CORS. You need to configure it intentionally, and if you get lazy with wildcards or credentials, you can open up more access than you meant to. ...
CORS gets weird at the edge. On a normal app server, you usually control one thing: the response. At the edge, you control the response, the cache key, sometimes the request headers, and sometimes a chain of proxies you barely remember setting up six months ago. That’s where small CORS mistakes turn into “works in curl, fails in browser” bugs. This guide is the version I wish I had the first few times I debugged CORS on a CDN or edge worker. ...