解决Flask和Web应用在Docker服务器上跨域请求(CORS)问题

Access to fetch at 'https://backend.apps.company.com/hello' from
origin 'https://frontend.apps.company.com' has been blocked by CORS policy: 
Response to preflight request doesn't pass access control check: 
No 'Access-Control-Allow-Origin' header is present on the requested resource

server {
    listen 9080; # 前端监听端口
    server_name frontend.apps.company.com; # 前端域名

    location / {
        root /usr/share/nginx/html;
        index index.html;
        try_files $uri $uri/ /index.html; # 处理单页应用路由
    }

    location /api {
        proxy_pass https://backend.apps.company.com; # 将/api请求转发到后端
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;

        # 启用CORS (可选，但建议配置)
        add_header 'Access-Control-Allow-Origin' "$http_origin" always;
        add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS' always;
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization' always;
        add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' always;

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

        proxy_http_version 1.1;
        proxy_request_buffering off;
        proxy_buffering off;
    }
}

from flask import Flask
from flask_cors import CORS

app = Flask(__name__)
# 允许来自任何域的跨域请求
CORS(app, supports_credentials=True)

@app.route("/hello")
def hello():
    return {"message": "Hello from backend!"}

if __name__ == '__main__':
    app.run(debug=True)