fix(cors): avoid overwriting Access-Control-Expose-Headers response header

apisix/plugins/cors.lua

@@ -75,11 +75,9 @@ local schema = {
         },
         expose_headers = {
             description =
-                "you can use '*' to expose all header when no credentials," ..
-                "'**' to allow forcefully(it will bring some security risks, be carefully)," ..
-                "multiple header use ',' to split. default: *.",
-            type = "string",
-            default = "*"
+                "multiple header use ',' to split." ..
+                "If not specified, no custom headers are exposed.",
+            type = "string"
         },
         max_age = {
             description =
@@ -226,7 +224,9 @@ local function set_cors_headers(conf, ctx)
     core.response.set_header("Access-Control-Allow-Origin", ctx.cors_allow_origins)
     core.response.set_header("Access-Control-Allow-Methods", allow_methods)
     core.response.set_header("Access-Control-Max-Age", conf.max_age)
-    core.response.set_header("Access-Control-Expose-Headers", conf.expose_headers)
+    if conf.expose_headers ~= nil and conf.expose_headers ~= "" then
+        core.response.set_header("Access-Control-Expose-Headers", conf.expose_headers)
+    end
     if conf.allow_headers == "**" then
         core.response.set_header("Access-Control-Allow-Headers",
             core.request.header(ctx, "Access-Control-Request-Headers"))

docs/en/latest/plugins/cors.md

@@ -39,7 +39,7 @@ The `cors` Plugins lets you enable [CORS](https://developer.mozilla.org/en-US/do
 | allow_origins             | string  | False    | "*"     | Origins to allow CORS. Use the `scheme://host:port` format. For example, `https://somedomain.com:8081`. If you have multiple origins, use a `,` to list them. If `allow_credential` is set to `false`, you can enable CORS for all origins by using `*`. If `allow_credential` is set to `true`, you can forcefully allow CORS on all origins by using `**` but it will pose some security issues. |
 | allow_methods             | string  | False    | "*"     | Request methods to enable CORS on. For example `GET`, `POST`. Use `,` to add multiple methods. If `allow_credential` is set to `false`, you can enable CORS for all methods by using `*`. If `allow_credential` is set to `true`, you can forcefully allow CORS on all methods by using `**` but it will pose some security issues.                                                                |
 | allow_headers             | string  | False    | "*"     | Headers in the request allowed when accessing a cross-origin resource. Use `,` to add multiple headers. If `allow_credential` is set to `false`, you can enable CORS for all request headers by using `*`. If `allow_credential` is set to `true`, you can forcefully allow CORS on all request headers by using `**` but it will pose some security issues.                                       |
-| expose_headers            | string  | False    | "*"     | Headers in the response allowed when accessing a cross-origin resource. Use `,` to add multiple headers. If `allow_credential` is set to `false`, you can enable CORS for all response headers by using `*`. If `allow_credential` is set to `true`, you can forcefully allow CORS on all response headers by using `**` but it will pose some security issues.                                    |
+| expose_headers            | string  | False    |         | Headers in the response allowed when accessing a cross-origin resource. Use `,` to add multiple headers. If `allow_credential` is set to `false`, you can enable CORS for all response headers by using `*`. If not specified, the plugin will not modify the `Access-Control-Expose-Headers header`. See [Access-Control-Expose-Headers - MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Expose-Headers) for more details.  |
 | max_age                   | integer | False    | 5       | Maximum time in seconds the result is cached. If the time is within this limit, the browser will check the cached result. Set to `-1` to disable caching. Note that the maximum value is browser dependent. See [Access-Control-Max-Age](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Max-Age#Directives) for more details.                                            |
 | allow_credential          | boolean | False    | false   | When set to `true`, allows requests to include credentials like cookies. According to CORS specification, if you set this to `true`, you cannot use '*' to allow all for the other attributes.                                                                                                                                                                                                     |
 | allow_origins_by_regex    | array   | False    | nil     | Regex to match origins that allow CORS. For example, `[".*\.test.com$"]` can match all subdomains of `test.com`. When set to specified range, only domains in this range will be allowed, no matter what `allow_origins` is.                                                                                                                                                                   |
@@ -110,7 +110,6 @@ curl http://127.0.0.1:9080/hello -v
 < Access-Control-Allow-Origin: *
 < Access-Control-Allow-Methods: *
 < Access-Control-Allow-Headers: *
-< Access-Control-Expose-Headers: *
 < Access-Control-Max-Age: 5
 ...
 ```

docs/zh/latest/plugins/cors.md

@@ -37,7 +37,7 @@ description: 本文介绍了 Apache APISIX cors 插件的基本信息及使用
 | allow_origins    | string  | 否   | "*"    | 允许跨域访问的 Origin，格式为 `scheme://host:port`，示例如 `https://somedomain.com:8081`。如果你有多个 Origin，请使用 `,` 分隔。当 `allow_credential` 为 `false` 时，可以使用 `*` 来表示允许所有 Origin 通过。你也可以在启用了 `allow_credential` 后使用 `**` 强制允许所有 Origin 均通过，但请注意这样存在安全隐患。 |
 | allow_methods    | string  | 否   | "*"    | 允许跨域访问的 Method，比如：`GET`，`POST` 等。如果你有多个 Method，请使用 `,` 分割。当 `allow_credential` 为 `false` 时，可以使用 `*` 来表示允许所有 Method 通过。你也可以在启用了 `allow_credential` 后使用 `**` 强制允许所有 Method 都通过，但请注意这样存在安全隐患。 |
 | allow_headers    | string  | 否   | "*"    | 允许跨域访问时请求方携带哪些非 `CORS 规范` 以外的 Header。如果你有多个 Header，请使用 `,` 分割。当 `allow_credential` 为 `false` 时，可以使用 `*` 来表示允许所有 Header 通过。你也可以在启用了 `allow_credential` 后使用 `**` 强制允许所有 Header 都通过，但请注意这样存在安全隐患。 |
-| expose_headers   | string  | 否   | "*"    | 允许跨域访问时响应方携带哪些非 `CORS 规范` 以外的 Header。如果你有多个 Header，请使用 `,` 分割。当 `allow_credential` 为 `false` 时，可以使用 `*` 来表示允许任意 Header。你也可以在启用了 `allow_credential` 后使用 `**` 强制允许任意 Header，但请注意这样存在安全隐患。 |
+| expose_headers   | string  | 否   |        | 允许跨域访问时响应方携带哪些非 CORS 规范 以外的 Header。如果你有多个 Header，请使用 , 分割。当 allow_credential 为 false 时，可以使用 * 来表示允许任意 Header。如果不设置，插件不会修改 `Access-Control-Expose-Headers` 头，详情请参考 [Access-Control-Expose-Headers - MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Expose-Headers)。 |
 | max_age          | integer | 否   | 5      | 浏览器缓存 CORS 结果的最大时间，单位为秒。在这个时间范围内，浏览器会复用上一次的检查结果，`-1` 表示不缓存。请注意各个浏览器允许的最大时间不同，详情请参考 [Access-Control-Max-Age - MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Max-Age#directives)。 |
 | allow_credential | boolean | 否   | 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`，那么将不能在其他属性中使用 `*`。 |
 | allow_origins_by_regex | array | 否   | nil  | 使用正则表达式数组来匹配允许跨域访问的 Origin，如 `[".*\.test.com$"]` 可以匹配任何 `test.com` 的子域名。如果 `allow_origins_by_regex` 属性已经指定，则会忽略 `allow_origins` 属性。 |
@@ -94,7 +94,6 @@ curl http://127.0.0.1:9080/hello -v
 < Access-Control-Allow-Origin: *
 < Access-Control-Allow-Methods: *
 < Access-Control-Allow-Headers: *
-< Access-Control-Expose-Headers: *
 < Access-Control-Max-Age: 5
 ...
 ```

t/plugin/cors.t

@@ -235,7 +235,7 @@ Access-Control-Allow-Origin: *
 Vary:
 Access-Control-Allow-Methods: *
 Access-Control-Allow-Headers: *
-Access-Control-Expose-Headers: *
+Access-Control-Expose-Headers:
 Access-Control-Max-Age: 5
 Access-Control-Allow-Credentials:
 

t/plugin/cors3.t

@@ -185,7 +185,7 @@ Access-Control-Allow-Origin: https://test.com
 Vary: Via, Origin
 Access-Control-Allow-Methods: *
 Access-Control-Allow-Headers: *
-Access-Control-Expose-Headers: *
+Access-Control-Expose-Headers:
 Access-Control-Max-Age: 5
 Access-Control-Allow-Credentials:
 
@@ -204,7 +204,7 @@ Access-Control-Allow-Origin: https://domain.com
 Vary: Via, Origin
 Access-Control-Allow-Methods: *
 Access-Control-Allow-Headers: *
-Access-Control-Expose-Headers: *
+Access-Control-Expose-Headers:
 Access-Control-Max-Age: 5
 Access-Control-Allow-Credentials:
 
@@ -276,7 +276,7 @@ Access-Control-Allow-Origin: https://domain.com
 Vary: Via, Origin
 Access-Control-Allow-Methods: *
 Access-Control-Allow-Headers: *
-Access-Control-Expose-Headers: *
+Access-Control-Expose-Headers:
 Access-Control-Max-Age: 5
 Access-Control-Allow-Credentials:
 
@@ -295,7 +295,7 @@ Access-Control-Allow-Origin: https://sub.domain.com
 Vary: Via, Origin
 Access-Control-Allow-Methods: *
 Access-Control-Allow-Headers: *
-Access-Control-Expose-Headers: *
+Access-Control-Expose-Headers:
 Access-Control-Max-Age: 5
 Access-Control-Allow-Credentials:
 
@@ -348,7 +348,7 @@ Access-Control-Allow-Origin: http://foo.example.org
 Vary: Origin
 Access-Control-Allow-Methods: *
 Access-Control-Allow-Headers: *
-Access-Control-Expose-Headers: *
+Access-Control-Expose-Headers:
 Access-Control-Max-Age: 5
 Access-Control-Allow-Credentials:
 
@@ -417,6 +417,6 @@ hello world
 Access-Control-Allow-Origin: https://domain.com
 Access-Control-Allow-Methods: *
 Access-Control-Allow-Headers: *
-Access-Control-Expose-Headers: *
+Access-Control-Expose-Headers:
 Access-Control-Max-Age: 5
 Access-Control-Allow-Credentials:

t/plugin/cors4.t

@@ -639,3 +639,113 @@ Access-Control-Allow-Headers: request-h
 Access-Control-Expose-Headers: expose-h
 Access-Control-Max-Age: 10
 Timing-Allow-Origin: http://testurl.domain.com
+
+
+
+=== TEST 26: set route ( expose_headers not specified )
+--- config
+    location /t {
+        content_by_lua_block {
+            local t = require("lib.test_admin").test
+            local code, body = t('/apisix/admin/routes/1',
+                 ngx.HTTP_PUT,
+                 [[{
+                    "plugins": {
+                        "cors": {
+                            "allow_credential": true,
+                            "allow_headers": "**",
+                            "allow_methods": "**",
+                            "allow_origins": "**",
+                            "expose_headers": "",
+                            "max_age": 3500
+                        }
+                    },
+                    "upstream": {
+                        "nodes": {
+                            "127.0.0.1:1980": 1
+                        },
+                        "type": "roundrobin"
+                    },
+                    "uri": "/hello"
+                }]]
+                )
+            if code >= 300 then
+                ngx.status = code
+            end
+            ngx.say(body)
+        }
+    }
+--- request
+GET /t
+--- response_body
+passed
+
+
+
+=== TEST 27: remove Access-Control-Expose-Headers match
+--- request
+GET /hello HTTP/1.1
+--- more_headers
+Origin: http://sub.domain.com
+--- response_headers
+Access-Control-Allow-Origin: http://sub.domain.com
+Access-Control-Allow-Methods: GET,POST,PUT,DELETE,PATCH,HEAD,OPTIONS,CONNECT,TRACE
+Access-Control-Expose-Headers:
+Access-Control-Allow-Headers:
+Access-Control-Max-Age: 3500
+Access-Control-Allow-Credentials: true
+
+
+
+=== TEST 28: set route ( expose_headers set value )
+--- config
+    location /t {
+        content_by_lua_block {
+            local t = require("lib.test_admin").test
+            local code, body = t('/apisix/admin/routes/1',
+                 ngx.HTTP_PUT,
+                 [[{
+                    "plugins": {
+                        "cors": {
+                            "allow_credential": true,
+                            "allow_headers": "**",
+                            "allow_methods": "**",
+                            "allow_origins": "**",
+                            "expose_headers": "ex-headr1,ex-headr2",
+                            "max_age": 3500
+                        }
+                    },
+                    "upstream": {
+                        "nodes": {
+                            "127.0.0.1:1980": 1
+                        },
+                        "type": "roundrobin"
+                    },
+                    "uri": "/hello"
+                }]]
+                )
+            if code >= 300 then
+                ngx.status = code
+            end
+            ngx.say(body)
+        }
+    }
+--- request
+GET /t
+--- response_body
+passed
+
+
+
+=== TEST 29: Access-Control-Expose-Headers match
+--- request
+GET /hello HTTP/1.1
+--- more_headers
+Origin: http://sub.domain.com
+--- response_headers
+Access-Control-Allow-Origin: http://sub.domain.com
+Access-Control-Allow-Methods: GET,POST,PUT,DELETE,PATCH,HEAD,OPTIONS,CONNECT,TRACE
+Access-Control-Expose-Headers: ex-headr1,ex-headr2
+Access-Control-Allow-Headers:
+Access-Control-Max-Age: 3500
+Access-Control-Allow-Credentials: true