Add support for bearer auth (#1488)

docs/basic-config.asciidoc

@@ -67,6 +67,13 @@ auth: {
   apiKey: 'base64EncodedKey'
 }
 ----
+Bearer authentication, useful for https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-create-service-token.html[service account tokens]. Be aware that it does not handle automatic token refresh:
+[source,js]
+----
+auth: {
+  bearer: 'token'
+}
+----
 
 
 |`maxRetries`
@@ -248,4 +255,4 @@ const client = new Client({
 |`boolean`, `'proto'`, `'constructor'` - By the default the client will protect you against prototype poisoning attacks. Read https://web.archive.org/web/20200319091159/https://hueniverse.com/square-brackets-are-the-enemy-ff5b9fd8a3e8?gi=184a27ee2a08[this article] to learn more. If needed you can disable prototype poisoning protection entirely or one of the two checks. Read the `secure-json-parse` https://github.com/fastify/secure-json-parse[documentation] to learn more. +
 _Default:_ `false`
 
-|===
+|===

docs/connecting.asciidoc

@@ -93,6 +93,26 @@ const client = new Client({
 })
 ----
 
+[discrete]
+[[auth-bearer]]
+==== Bearer authentication
+
+You can provide your credentials by passing the `bearer` token
+parameter via the `auth` option.
+Useful for https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-create-service-token.html[service account tokens].
+Be aware that it does not handle automatic token refresh.
+
+[source,js]
+----
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({
+  node: 'https://localhost:9200',
+  auth: {
+    bearer: 'token'
+  }
+})
+----
+
 
 [discrete]
 [[auth-basic]]