Add missed reverse proxy authentication documentation

docs/content/doc/features/authentication.en-us.md

@@ -329,3 +329,22 @@ Before activating SSPI single sign-on authentication (SSO) you have to prepare y
   - You have added the URL of the web app to the `Local intranet zone`
   - The clocks of the server and client should not differ with more than 5 minutes (depends on group policy)
   - `Integrated Windows Authentication` should be enabled in Internet Explorer (under `Advanced settings`)
+
+## Reverse Proxy
+
+Gitea supports Reverse Proxy Header authentication, it will read headers as a trusted login user name or user email address. This hasn't been enabled default, you can enable it with
+
+```ini
+[service]
+ENABLE_REVERSE_PROXY_AUTHENTICATION = true
+```
+
+The default login user name is in the `X-WEBAUTH-USER` header, you can change it via changing `REVERSE_PROXY_AUTHENTICATION_USER` in app.ini. If the user doesn't exist, you can enable automatic registration with `ENABLE_REVERSE_PROXY_AUTO_REGISTRATION=true`.
+
+The default login user email is `X-WEBAUTH-EMAIL`, you can change it via changing `REVERSE_PROXY_AUTHENTICATION_EMAIL` in app.ini, this could also be disabled with `ENABLE_REVERSE_PROXY_EMAIL`
+
+If set `ENABLE_REVERSE_PROXY_FULL_NAME=true`, a user full name expected in `X-WEBAUTH-FULLNAME` will be assigned to the user when auto creating the user. You can also change the header name with `REVERSE_PROXY_AUTHENTICATION_FULL_NAME`.
+
+You can also limit the reverse proxy's IP address range with `REVERSE_PROXY_TRUSTED_PROXIES` which default value is `127.0.0.0/8,::1/128`. By `REVERSE_PROXY_LIMIT`, you can limit trusted proxies level.
+
+Notice: Reverse Proxy Auth doesn't support authenticate API, you still need an access token or basic auth to visit API.

docs/content/doc/features/authentication.zh-cn.md

@@ -15,4 +15,21 @@ menu:
 
 # 认证
 
-## TBD
+## 反向代理认证
+
+Gitea 支持通过读取反向代理传递的HTTP 头中的登录名或者email地址来支持反向代理来认证。默认是不器用的，你可以用一下配置启用。
+
+```ini
+[service]
+ENABLE_REVERSE_PROXY_AUTHENTICATION = true
+```
+
+默认的登录用户名的 HTTP 头是 `X-WEBAUTH-USER`，你可以通过修改 `REVERSE_PROXY_AUTHENTICATION_USER` 来变更它。如果用户不存在，可以自动创建用户，当然你需要修改 `ENABLE_REVERSE_PROXY_AUTO_REGISTRATION=true` 来启用它。
+
+默认的登录用户Email的 HTTP 头是 `X-WEBAUTH-EMAIL`，你可以通过修改 `REVERSE_PROXY_AUTHENTICATION_EMAIL` 来变更它。如果用户不存在，可以自动创建用户，当然你需要修改 `ENABLE_REVERSE_PROXY_AUTO_REGISTRATION=true` 来启用它。你也可以通过修改 `ENABLE_REVERSE_PROXY_EMAIL` 来启用或停用这个 HTTP 头。
+
+如果设置了 `ENABLE_REVERSE_PROXY_FULL_NAME=true`，则用户的全名会从 `X-WEBAUTH-FULLNAME` 读取，这样在自动创建用户时将使用这个字段作为用户全名，你也可以通过修改 `REVERSE_PROXY_AUTHENTICATION_FULL_NAME` 来变更 HTTP 头。
+
+你也可以通过修改 `REVERSE_PROXY_TRUSTED_PROXIES` 来设置反向代理的IP地址范围，加强安全性，默认值是 `127.0.0.0/8,::1/128`。 通过 `REVERSE_PROXY_LIMIT`， 可以设置最多信任几级反向代理。
+
+注意：反向代理认证不支持认证 API，API仍旧需要用access token来进行认证。