Add English translation of the key_rate_limit extension. (#118)

plugins/wasm-cpp/extensions/key_rate_limit/README.md

@@ -1,3 +1,7 @@
+<p>
+   <a href="README_EN.md"> English </a> | 中文
+</p>
+
 # 功能说明
 `key-rate-limit`插件实现了基于特定键值实现限流，键值来源可以是 URL 参数、HTTP 请求头
 

plugins/wasm-cpp/extensions/key_rate_limit/README_EN.md

@@ -0,0 +1,70 @@
+<p>
+   English | <a href="README.md">中文</a>
+</p>
+
+# Description
+`key-rate-limit` plugin implements a rate-limiting function based on specific key-values. The key-values may come from URL parameters or HTTP headers.
+
+# Configuration Fields
+
+| Name | Type | Requirement |  Default Value | Description |
+| -------- | -------- | -------- | -------- | -------- |
+|  limit_by_header     |  string     | Optional. Choose one from following: `limit_by_header`, `limit_by_param`. |   -  |  The name of HTTP header used to obtain key-value used in rate-limiting. |
+|  limit_by_param     |  string     | Optional. Choose one from following: `limit_by_header`, `limit_by_param`. |   -  |  The name of URL parameter used to obtain key-value used in rate-limiting.   |
+|  limit_keys     |  array of object     | Required     |   -  |  Rate-limiting thresholds when matching specific key-values |
+
+Field descriptions of `limit_keys` items:
+| Name | Type | Requirement |  Default Value | Description |
+| -------- | -------- | -------- | -------- | -------- |
+|  key     |  string     | Required     |   -  |  Value to match of the specific key |
+|  query_per_second     |  number     | Optional. Choose one from following: `query_per_second`, `query_per_minute`, `query_per_hour`, `query_per_day`. |   -  |  Number of requests allowed per second |
+|  query_per_minute     |  number     | Optional. Choose one from following: `query_per_second`, `query_per_minute`, `query_per_hour`, `query_per_day`. |   -  |  Number of requests allowed per minute |
+|  query_per_hour     |  number     | Optional. Choose one from following: `query_per_second`, `query_per_minute`, `query_per_hour`, `query_per_day`. |   -  |  Number of requests allowed per hour |
+|  query_per_day     |  number     | Optional. Choose one from following: `query_per_second`, `query_per_minute`, `query_per_hour`, `query_per_day`. |   -  |  Number of requests allowed per day |
+
+# Configuration Samples
+
+## Use query parameter `apikey` for rate-limiting
+```yaml
+limit_by_param: apikey
+limit_keys:
+- key: 9a342114-ba8a-11ec-b1bf-00163e1250b5
+  query_per_second: 10
+- key: a6a6d7f2-ba8a-11ec-bec2-00163e1250b5
+  query_per_minute: 100
+```
+
+## Use HTTP header parameter `x-ca-key` for rate-limiting
+```yaml
+limit_by_header: x-ca-key
+limit_keys:
+- key: 102234
+  query_per_second: 10
+- key: 308239
+  query_per_hour: 10
+```
+
+## Enable rate-limiting for specific routes or domains
+```yaml
+# Use _rules_ field for fine-grained rule configurations
+_rules_:
+# Rule 1: Match by route name
+- _match_route_:
+  - route-a
+  - route-b
+  limit_by_header: x-ca-key
+  limit_keys:
+  - key: 102234
+    query_per_second: 10
+# Rule 2: Match by domain
+- _match_domain_:
+  - "*.example.com"
+  - test.com
+  limit_by_header: x-ca-key
+  limit_keys:
+  - key: 102234
+    query_per_second: 100
+```
+In the rule sample of `_match_route_`, `route-a` and `route-b` are the route names provided when creating a new gateway route. When the current route names matches the configuration, the rule following shall be applied.
+In the rule sample of `_match_domain_`, `*.example.com` and `test.com` are the domain names used for request matching. When the current domain name matches the configuration, the rule following shall be applied.
+All rules shall be checked following the order of items in the `_rules_` field，The first matched rule will be applied. All remained will be ignored.