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API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) · レッスン

Cross-Origin Resource Sharing（CORS）

NginxでCORSポリシーを実装し、APIへの安全なクロスドメインリクエストを可能にします。

「Cross-Origin Resource Sharing（CORS）」はCoddyKit上の無料API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)レッスンです。 これはレッスン2/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはAPI Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)コースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

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.

よくある質問

「Cross-Origin Resource Sharing（CORS）」レッスンは無料ですか？

はい。「Cross-Origin Resource Sharing（CORS）」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)コースには全4レッスンが含まれています。

「Cross-Origin Resource Sharing（CORS）」で何を学びますか？

NginxでCORSポリシーを実装し、APIへの安全なクロスドメインリクエストを可能にします。 ブラウザで直接実行するハンズオンコードでAPI Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)を始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのAPI Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン2/4です。

「Cross-Origin Resource Sharing（CORS）」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このAPI Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)レッスンでコードを書いて実行できますか？

はい。すべてのAPI Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

  1. NginxによるAPIバージョニング
  2. Cross-Origin Resource Sharing（CORS）
  3. Nginxによるレート制限とスロットリング
  4. パスベースのマイクロサービスルーティング
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