Added proxy support (#1260)

docs/configuration.asciidoc

@@ -117,6 +117,24 @@ _Default:_ `false`
 |`http.SecureContextOptions` - ssl https://nodejs.org/api/tls.html[configuraton]. +
 _Default:_ `null`
 
+|`proxy`
+a|`string, URL` - If you are using an http(s) proxy, you can put its url here.
+The client will automatically handle the connection to it. +
+_Default:_ `null`
+[source,js]
+----
+const client = new Client({
+  node: 'http://localhost:9200',
+  proxy: 'http://localhost:8080'
+})
+
+// Proxy with basic authentication
+const client = new Client({
+  node: 'http://localhost:9200',
+  proxy: 'http://user:pwd@localhost:8080'
+})
+----
+
 |`agent`
 a|`http.AgentOptions, function` - http agent https://nodejs.org/api/http.html#http_new_agent_options[options], 
 or a function that returns an actual http agent instance. If you want to disable the http agent use entirely

docs/usage.asciidoc

@@ -210,6 +210,45 @@ _Default:_ `null`
 _Default:_ `null`
 |===
 
+=== Connecting through a proxy
+
+~Added~ ~in~ ~`v7.10.0`~
+
+If you need to pass through an http(s) proxy for connecting to Elasticsearch, the client offers
+out of the box a handy configuration for helping you with it. Under the hood it
+uses the https://github.com/delvedor/hpagent[`hpagent`] module.
+
+[source,js]
+----
+const client = new Client({
+  node: 'http://localhost:9200',
+  proxy: 'http://localhost:8080'
+})
+----
+
+Basic authentication is supported as well:
+
+[source,js]
+----
+const client = new Client({
+  node: 'http://localhost:9200',
+  proxy: 'http:user:pwd@//localhost:8080'
+})
+----
+
+If you are connecting through a not http(s) proxy, such as a `socks5` or `pac`,
+you can use the `agent` option to configure it.
+
+[source,js]
+----
+const SocksProxyAgent = require('socks-proxy-agent')
+const client = new Client({
+  node: 'http://localhost:9200',
+  agent () {
+    return new SocksProxyAgent('socks://127.0.0.1:1080')
+  }
+})
+----
 
 === Error handling