# 功能说明

`cors` 插件可以为服务端启用 CORS（Cross-Origin Resource Sharing，跨域资源共享）的返回 http 响应头。

# 配置字段

| 名称                    | 数据类型         | 填写要求  | 默认值                                                                                                                       | 描述                                                                                                                                                                           |
|-----------------------|-----------------|-------|---------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| allow_origins         | array of string | 选填    | *                                                                                                                         | 允许跨域访问的 Origin，格式为 scheme://host:port，示例如 http://example.com:8081。当 allow_credentials 为 false 时，可以使用 * 来表示允许所有 Origin 通过                                                     |
| allow_origin_patterns | array of string | 选填    | -                                                                                                                         | 允许跨域访问的 Origin 模式匹配， 用 * 匹配域名或者端口， <br/>比如 http://*.example.com -- 匹配域名， http://*.example.com:[8080,9090] -- 匹配域名和指定端口， http://*.example.com:[*] -- 匹配域名和所有端口。单独 * 表示匹配所有域名和端口 |
| allow_methods         | array of string | 选填    | GET, PUT, POST, DELETE, PATCH, OPTIONS                                                                                    | 允许跨域访问的 Method，比如：GET，POST 等。可以使用 * 来表示允许所有 Method。                                                                                                                          |
| allow_headers         | array of string | 选填    | DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With，<br/>If-Modified-Since,Cache-Control,Content-Type,Authorization | 允许跨域访问时请求方携带哪些非 CORS 规范以外的 Header。可以使用 * 来表示允许任意 Header。                                                                                                                     |
| expose_headers        | array of string | 选填    | -                                                                                                                         | 允许跨域访问时响应方携带哪些非 CORS 规范以外的 Header。可以使用 * 来表示允许任意 Header。                                                                                                                     |
| allow_credentials     | bool            | 选填    | false                                                                                                                     | 是否允许跨域访问的请求方携带凭据（如 Cookie 等）。根据 CORS 规范，如果设置该选项为 true，在 allow_origins 不能使用 *， 替换成使用 allow_origin_patterns *                                                                  |
| max_age               | number          | 选填    | 86400秒                                                                                                                     | 浏览器缓存 CORS 结果的最大时间，单位为秒。<br/>在这个时间范围内，浏览器会复用上一次的检查结果                                                                                                                         |

> 注意
> * allow_credentials 是一个很敏感的选项，请谨慎开启。开启之后，allow_credentials 和 allow_origins 为 * 不能同时使用，同时设置时， allow_origins 值为 "*" 生效。
> * allow_origins 和 allow_origin_patterns 可以同时设置， 先检查 allow_origins 是否匹配，然后再检查 allow_origin_patterns 是否匹配
> * 非法 CORS 请求， HTTP 状态码返回是 403， 返回体内容为 "Invalid CORS request"

# 配置示例

## 允许所有跨域访问, 不允许请求方携带凭据
```yaml
allow_origins:
  - '*'
allow_methods:
  - '*'  
allow_headers:
  - '*'
expose_headers:
  - '*'
allow_credentials: false
max_age: 7200
```

## 允许所有跨域访问,同时允许请求方携带凭据
```yaml
allow_origin_patterns:
  - '*'
allow_methods:
  - '*'  
allow_headers:
  - '*'
expose_headers:
  - '*'
allow_credentials: true
max_age: 7200
```

## 允许特定子域,特定方法，特定请求头跨域访问，同时允许请求方携带凭据
```yaml
allow_origin_patterns:
  - http://*.example.com
  - http://*.example.org:[8080,9090]
allow_methods:
  - GET
  - PUT
  - POST
  - DELETE
allow_headers:
  - Token
  - Content-Type
  - Authorization
expose_headers:
  - '*'
allow_credentials: true
max_age: 7200
```

# 测试

## 测试配置

```yaml
apiVersion: networking.higress.io/v1
kind: McpBridge
metadata:
  name: mcp-cors-httpbin
  namespace: higress-system
spec:
  registries:
    - domain: httpbin.org
      name: httpbin
      port: 80
      type: dns
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    higress.io/destination: httpbin.dns
    higress.io/upstream-vhost: "httpbin.org"
    higress.io/backend-protocol: HTTP
  name: ingress-cors-httpbin
  namespace: higress-system
spec:
  ingressClassName: higress
  rules:
    - host: httpbin.example.com
      http:
        paths:
          - backend:
              resource:
                apiGroup: networking.higress.io
                kind: McpBridge
                name: mcp-cors-httpbin
            path: /
            pathType: Prefix
---
apiVersion: extensions.higress.io/v1alpha1
kind: WasmPlugin
metadata:
  name: wasm-cors-httpbin
  namespace: higress-system
spec:
  defaultConfigDisable: true
  matchRules:
    - config:
        allow_origins:
          - http://httpbin.example.net
        allow_origin_patterns:
          - http://*.example.com:[*]
          - http://*.example.org:[9090,8080]
        allow_methods:
          - GET
          - POST
          - PATCH
        allow_headers:
          - Content-Type
          - Token
          - Authorization
        expose_headers:
          - X-Custom-Header
          - X-Env-UTM
        allow_credentials: true
        max_age: 3600
      configDisable: false
      ingress:
        - ingress-cors-httpbin
  url: oci://higress-registry.cn-hangzhou.cr.aliyuncs.com/plugins/cors:1.0.0
  imagePullPolicy: Always
```

## 请求测试

### 简单请求
```shell
curl -v -H "Origin: http://httpbin2.example.org:9090" -H  "Host: httpbin.example.com"  http://127.0.0.1/anything/get\?foo\=1

< HTTP/1.1 200 OK
> x-cors-version: 1.0.0
> access-control-allow-origin: http://httpbin2.example.org:9090
> access-control-expose-headers: X-Custom-Header,X-Env-UTM
> access-control-allow-credentials: true
```

### 预检请求

```shell
curl -v -X OPTIONS -H "Origin: http://httpbin2.example.org:9090" -H  "Host: httpbin.example.com" -H "Access-Control-Request-Method: POST"  -H "Access-Control-Request-Headers: Content-Type, Token" http://127.0.0.1/anything/get\?foo\=1

< HTTP/1.1 200 OK
< x-cors-version: 1.0.0
< access-control-allow-origin: http://httpbin2.example.org:9090
< access-control-allow-methods: GET,POST,PATCH
< access-control-allow-headers: Content-Type,Token,Authorization
< access-control-expose-headers: X-Custom-Header,X-Env-UTM
< access-control-allow-credentials: true
< access-control-max-age: 3600
< date: Tue, 23 May 2023 11:41:28 GMT
< server: istio-envoy
< content-length: 0
<
* Connection #0 to host 127.0.0.1 left intact
* Closing connection 0
```

### 非法 CORS Origin 预检请求

```shell
curl -v -X OPTIONS -H "Origin: http://httpbin2.example.org" -H  "Host: httpbin.example.com" -H "Access-Control-Request-Method: GET"  http://127.0.0.1/anything/get\?foo\=1

 HTTP/1.1 403 Forbidden
< content-length: 70
< content-type: text/plain
< x-cors-version: 1.0.0
< date: Tue, 23 May 2023 11:27:01 GMT
< server: istio-envoy
<
* Connection #0 to host 127.0.0.1 left intact
Invalid CORS request
```

### 非法 CORS Method 预检请求

```shell
curl -v -X OPTIONS -H "Origin: http://httpbin2.example.org:9090" -H  "Host: httpbin.example.com" -H "Access-Control-Request-Method: DELETE"  http://127.0.0.1/anything/get\?foo\=1

< HTTP/1.1 403 Forbidden
< content-length: 49
< content-type: text/plain
< x-cors-version: 1.0.0
< date: Tue, 23 May 2023 11:28:51 GMT
< server: istio-envoy
<
* Connection #0 to host 127.0.0.1 left intact
Invalid CORS request
```

### 非法 CORS Header 预检请求

```shell
 curl -v -X OPTIONS -H "Origin: http://httpbin2.example.org:9090" -H  "Host: httpbin.example.com" -H "Access-Control-Request-Method: GET" -H "Access-Control-Request-Headers: TokenView"  http://127.0.0.1/anything/get\?foo\=1

< HTTP/1.1 403 Forbidden
< content-length: 52
< content-type: text/plain
< x-cors-version: 1.0.0
< date: Tue, 23 May 2023 11:31:03 GMT
< server: istio-envoy
<
* Connection #0 to host 127.0.0.1 left intact
Invalid CORS request
```

# 参考文档
- https://www.ruanyifeng.com/blog/2016/04/cors.html
- https://fetch.spec.whatwg.org/#http-cors-protocol