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API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) · Lezione

Cross-Origin Resource Sharing (CORS)

Implementi policy CORS in Nginx per consentire richieste sicure tra domini diversi per le proprie API.

Cross-Origin Resource Sharing (CORS) è una lezione API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) gratuita su CoddyKit. Questa è la lezione 2 di 4. Puoi leggere la lezione completa qui gratuitamente — poi esercitati direttamente nel browser con un editor di codice integrato e un tutor IA disponibile 24/7. Fa parte del percorso di apprendimento API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway), e i tuoi progressi si sincronizzano tra il web e l'app CoddyKit. Il corso API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) include 4 lezioni in totale.

Parti di questa lezione non sono ancora state tradotte e vengono mostrate in inglese.

What is CORS?

Imagine you're building a web application. Your frontend (like a React app) runs on app.example.com, but it needs to fetch data from your API running on api.example.com.

This is where Cross-Origin Resource Sharing (CORS) comes in. It's a security feature implemented by web browsers to control how web pages from one origin can request resources from another origin.

The Same-Origin Policy

CORS is a relaxation of the browser's Same-Origin Policy. This policy is a critical security mechanism that prevents a malicious website from reading sensitive data from another site.

  • Origin is defined by the protocol, host, and port.
  • https://app.example.com:443 is different from http://app.example.com:80 or https://api.example.com:443.

Without CORS, browsers would block your frontend from talking to your API because they have different origins.

How CORS Works

When your browser detects a cross-origin request, it adds an Origin header to the request. The server then needs to respond with specific CORS headers to tell the browser it's allowed.

The most important header is Access-Control-Allow-Origin. If this header is present in the server's response and its value matches the client's origin (or is *), the browser allows the request.

Simple vs. Preflight Requests

CORS requests can be categorized into two types:

  • Simple Requests: These are direct GET, HEAD, or POST requests with specific content types (like text/plain). The browser sends them immediately, expecting CORS headers in the response.
  • Preflight Requests: For more complex requests (e.g., PUT, DELETE, custom headers, or specific content types), the browser first sends an OPTIONS request. This 'preflight' checks with the server if the actual request is safe to send.

Nginx for CORS Headers

Since Nginx often acts as a reverse proxy or API gateway, it's the perfect place to manage CORS headers for your backend services. We can use Nginx directives to add the necessary Access-Control-* headers to responses.

The primary directive for this is add_header, which allows us to inject custom HTTP headers into Nginx responses.

Configuring Allow-Origin

Let's configure Nginx to allow requests from a specific origin, https://app.example.com, to your API.

We'll add the Access-Control-Allow-Origin header within a location block that handles your API requests.

server {
  listen 80;
  server_name api.example.com;

  location /api/ {
    add_header 'Access-Control-Allow-Origin' 'https://app.example.com';
    proxy_pass http://backend_api_service;
  }
}

Handling Multiple Origins

What if you have multiple frontends that need to access your API? You can't list multiple origins in Access-Control-Allow-Origin directly. Instead, you can use Nginx's map directive to dynamically set the header based on the incoming Origin header.

http {
  map $http_origin $cors_origin {
    default "";
    "https://app.example.com" "https://app.example.com";
    "https://dev.example.com" "https://dev.example.com";
  }

  server {
    listen 80;
    server_name api.example.com;

    location /api/ {
      if ($cors_origin ~ ".") {
        add_header 'Access-Control-Allow-Origin' $cors_origin;
      }
      proxy_pass http://backend_api_service;
    }
  }
}

Configuring Preflight Requests

For preflight (OPTIONS) requests, the browser expects specific headers in response to its OPTIONS call. Nginx needs to intercept these requests and respond with the appropriate CORS headers, often without proxying to the backend.

server {
  listen 80;
  server_name api.example.com;

  location /api/ {
    # Handle preflight OPTIONS requests
    if ($request_method = 'OPTIONS') {
      add_header 'Access-Control-Allow-Origin' 'https://app.example.com';
      add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, PUT, DELETE';
      add_header 'Access-Control-Allow-Headers' 'Content-Type, Authorization';
      add_header 'Access-Control-Max-Age' 1728000;
      add_header 'Content-Type' 'text/plain charset=UTF-8';
      add_header 'Content-Length' 0;
      return 204;
    }

    # For actual requests
    add_header 'Access-Control-Allow-Origin' 'https://app.example.com';
    proxy_pass http://backend_api_service;
  }
}

Essential CORS Headers

Beyond Access-Control-Allow-Origin, these headers are crucial for full CORS support:

  • Access-Control-Allow-Methods: Specifies allowed HTTP methods (e.g., GET, POST, PUT).
  • Access-Control-Allow-Headers: Lists headers the client is allowed to send (e.g., Content-Type, Authorization).
  • Access-Control-Allow-Credentials: Set to true if the client can send cookies or HTTP authentication.
  • Access-Control-Max-Age: How long the preflight response can be cached by the browser (in seconds).

Comprehensive CORS Setup

Here's a more complete Nginx configuration snippet that handles both simple and preflight CORS requests, allowing a specific origin to interact with your API, including sending credentials.

server {
  listen 80;
  server_name api.example.com;

  location /api/ {
    set $cors_origin "https://app.example.com"; # Or use map directive

    if ($request_method = 'OPTIONS') {
      add_header 'Access-Control-Allow-Origin' "$cors_origin";
      add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS';
      add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization';
      add_header 'Access-Control-Allow-Credentials' 'true';
      add_header 'Access-Control-Max-Age' 1728000;
      add_header 'Content-Type' 'text/plain charset=UTF-8';
      add_header 'Content-Length' 0;
      return 204;
    }

    add_header 'Access-Control-Allow-Origin' "$cors_origin";
    add_header 'Access-Control-Allow-Credentials' 'true';
    add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS';
    add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization';

    proxy_pass http://backend_api_service;
  }
}

CORS Header Check

Which of the following headers are essential for Nginx to respond correctly to a CORS preflight (OPTIONS) request?

Recap: Nginx CORS

In this lesson, you learned about Cross-Origin Resource Sharing (CORS) and why it's vital for secure web applications. We covered:

  • The Same-Origin Policy and why CORS exists.
  • The difference between simple and preflight requests.
  • How to configure Nginx using add_header and map directives to manage CORS.
  • Key CORS headers like Access-Control-Allow-Origin, Access-Control-Allow-Methods, Access-Control-Allow-Headers, and Access-Control-Max-Age.

Properly configuring CORS in Nginx ensures your frontend applications can securely communicate with your backend APIs across different domains.

Domande Frequenti

La lezione «Cross-Origin Resource Sharing (CORS)» è gratuita?

Sì — il testo completo di «Cross-Origin Resource Sharing (CORS)» è gratuito qui sul web. Per esercitarvi in modo interattivo (un editor di codice integrato e un tutor IA 24/7) e sbloccare il resto del corso API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway), passa a CoddyKit PRO. Il corso API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) include 4 lezioni in totale.

Cosa imparerò in «Cross-Origin Resource Sharing (CORS)»?

Implementi policy CORS in Nginx per consentire richieste sicure tra domini diversi per le proprie API. Eserciti API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) con codice pratico che esegui direttamente nel browser, e un tutor IA 24/7 risponde alle tue domande mentre lavori sulla lezione.

Ho bisogno di esperienza per iniziare API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)?

Non è richiesta alcuna esperienza precedente. API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) su CoddyKit è strutturato per principianti e studenti avanzati, quindi puoi iniziare da qui o dall'inizio e procedere al tuo ritmo. Questa è la lezione 2 di 4.

Quanto tempo richiede la lezione «Cross-Origin Resource Sharing (CORS)»?

La maggior parte delle lezioni CoddyKit richiede circa 5–10 minuti. Ogni lezione è breve e interattiva, quindi fai progressi costanti e riprendi esattamente da dove hai lasciato su web e app.

Posso scrivere ed eseguire codice in questa lezione API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)?

Sì. Ogni lezione API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) include un editor di codice integrato, quindi scrivi ed esegui codice reale direttamente nel tuo browser e ricevi feedback istantaneo dall'IA — nessuna configurazione locale necessaria.

Tutte le lezioni di questo corso

  1. Versionamento delle API con Nginx
  2. Cross-Origin Resource Sharing (CORS)
  3. Limitazione della frequenza e throttling con Nginx
  4. Routing basato sul path verso i microservizi
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