I’ve created an npm library that frontend developers can install and use on their websites. The library needs to make HTTP requests to my backend API server. The problem I’m facing is with CORS policy since different people will use my package on various websites with different domain names.
I can’t possibly maintain a list of all the domains that might use my package since it’s public. What’s the best approach to configure CORS on my server side to allow requests from any domain that uses my npm library? I want to avoid having users manually register their domains with me.
Is there a secure way to handle this situation without completely opening up my API with wildcard CORS settings?
honestly, just use access-control-allow-origin: * if your api’s already secured with keys. yeah, everyone says it’s bad practice, but if you’re validating tokens anyway, the origin doesn’t matter much. i’ve been running mine this way for 2+ years without issues.
I faced a similar challenge while developing an API library. To manage CORS effectively, I implemented token-based authentication. Whenever a user installs the library, they receive an API key. This key is then validated server-side for each request, allowing me to ease CORS restrictions while ensuring secure access. Additionally, you could consider automatically registering domains the first time an API key is used, which would create a dynamic whitelist without the need for manual input, keeping your API secure yet flexible.
The token approach works but you’re still stuck manually registering domains or dealing with messy server logic. I ran into this exact issue building integrations for multiple client sites.
I ended up moving the whole CORS mess to an automation platform. Instead of your npm library hitting your API directly, route everything through Latenode workflows.
Here’s the deal: Your library sends requests to Latenode endpoints instead of your backend. Latenode automatically handles CORS and forwards requests to your actual API. You can add auth, rate limiting, or validation logic right in the workflow without touching your main server.
Best part? Set up different workflows for different use cases. Some domains get premium features, others get basic access. All configurable through the visual workflow builder.
I’ve used this pattern for 8 months across different projects. Zero CORS issues and way more flexible than hardcoding domain lists or messing with server configs.
Dynamic CORS headers beat wildcards here. Skip the domain lists - just grab the Origin header from requests and set it as the allowed origin after your auth checks pass. Each response gets custom CORS headers for whatever domain actually made the request. I use middleware that validates API keys first, then sets Access-Control-Allow-Origin to match the request’s origin. Your server stays locked down with token validation but supports unlimited domains without any manual setup. Unlike wildcards, you’re still controlling access through proper auth while keeping CORS flexible. Handles preflight requests perfectly since the middleware treats OPTIONS the same way.
The dynamic CORS approach works but you’re still building custom middleware and dealing with edge cases. Auth, preflight handling, error responses - it gets messy quick.
I dropped all that by putting Latenode between my npm library and backend API. My library hits Latenode webhooks instead of my server directly. Latenode handles CORS from any domain, then forwards authenticated requests to my real API.
Here’s what’s powerful: the workflow layer. I validate API keys, transform request data, add logging, and cache responses - all visually without auth middleware. Different API keys trigger different workflows with different permissions or rate limits.
Your npm library stays simple. Backend stays clean. You get enterprise features like request monitoring and automatic retries without building them.
I made this switch after fighting CORS across 20+ client domains. Now I just update workflows when I need changes instead of deploying server code.
You’re encountering CORS (Cross-Origin Resource Sharing) issues when your npm library makes HTTP requests to your backend API. Different users install your library on websites with different domains, and you need a secure way to handle CORS without manually managing a whitelist of allowed origins or resorting to the insecure Access-Control-Allow-Origin: * wildcard.
Understanding the “Why” (The Root Cause):
CORS errors occur because browsers, for security reasons, restrict cross-origin requests. A cross-origin request is one where the origin (protocol, domain, and port) of the request differs from the origin of the resource being requested. Your npm library, running on a user’s website (Origin A), is making requests to your API server (Origin B). By default, the browser will block this unless your API server explicitly allows it. Using Access-Control-Allow-Origin: * disables this protection entirely, which is a major security risk.
The key is that you need a mechanism to verify the legitimacy of the request without needing to know the origin in advance.
Step-by-Step Guide:
Implement Origin Validation with API Key Verification: The most secure approach is to use API keys in conjunction with origin validation. This means your npm library will include an API key that needs to be passed with every request. Your backend will verify this key and use the Origin header from the request to set the Access-Control-Allow-Origin header dynamically in the response.
Here’s how it works:
Request: Your npm library sends a request to your API, including the API key in the headers (e.g., Authorization: Bearer <API_KEY>). It also includes the Origin header, which the browser automatically adds.
Backend (Server-Side Logic): Your API middleware or endpoint first validates the API key. If valid, it retrieves the Origin header from the request. If the Origin matches an expected pattern or is considered trustworthy (possibly based on other data you store associated with the API key), it sets the Access-Control-Allow-Origin header in the response to precisely that Origin. If invalid, a suitable error will be returned.
Response: The response from your API will contain the dynamically set Access-Control-Allow-Origin header, allowing the browser to accept the response. For preflight requests (OPTIONS requests), your server must handle the preflight appropriately to set the necessary Access-Control-Allow-Headers, Access-Control-Allow-Methods, etc., alongside the Access-Control-Allow-Origin header.
Secure API Key Management: Implement robust API key management practices. Consider rotating keys regularly and revoking keys if compromised. Never expose your API keys directly in your client-side code; they should only be used server-side for authentication.
Middleware Implementation (Example - Node.js with Express):
const express = require('express');
const app = express();
app.use((req, res, next) => {
const apiKey = req.headers.authorization;
const origin = req.headers.origin;
// Validate API Key (replace with your actual validation logic)
if (!apiKey || !isValidApiKey(apiKey)) {
return res.status(401).send('Unauthorized');
}
// Validate Origin (replace with your origin validation logic)
if (origin && isValidOrigin(origin, apiKey)) {
res.setHeader('Access-Control-Allow-Origin', origin);
}
res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE');
res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');
next();
});
// Your API routes
app.get('/api/data', (req, res) => {
// ... your API logic ...
});
app.listen(3000, () => console.log('Server listening on port 3000'));
// Placeholder functions (Replace with your actual implementation)
function isValidApiKey(apiKey) {
// Replace with your API key validation logic
return apiKey === 'YOUR_API_KEY';
}
function isValidOrigin(origin, apiKey){
//Replace with your origin validation logic.
//This example allows any origin if a valid API Key is provided
return true;
}
Common Pitfalls & What to Check Next:
Incorrect API Key Handling: Double-check that your npm library is correctly sending the API key with every request and that your backend is correctly parsing and validating it.
Origin Header Mismatch: Ensure your backend is correctly reading the Origin header from the request and not inadvertently using some other source.
Preflight Issues: If you’re using methods other than GET or POST, or custom headers, you’ll need to ensure your server correctly handles preflight OPTIONS requests.
Improper Header Setting: Confirm that the Access-Control-Allow-Origin header is being set correctly in the response by your server and that its value matches the request’s Origin header.
API Key Security: Regularly review and update your API key security measures.
Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!
Understanding the “Why” (The Root Cause):
Step-by-Step Guide:
Common Pitfalls & What to Check Next:
Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!