feat(outputs.elasticsearch): Allow settings extra headers for elasticsearch output (#15477)

plugins/outputs/elasticsearch/README.md

@@ -323,6 +323,11 @@ to use them.
   ## no pipeline is used for the metric.
   # use_pipeline = "{{es_pipeline}}"
   # default_pipeline = "my_pipeline"
+  #
+  # Custom HTTP headers
+  # To pass custom HTTP headers please define it in a given below section
+  # [outputs.elasticsearch.headers]
+  #    "X-Custom-Header" = "custom-value"
 ```
 
 ### Permissions
@@ -389,6 +394,8 @@ the `default_tag_value` will be used instead.
   instead.
 * `default_pipeline`: If dynamic pipeline names the tag does not exist in a
   particular metric, this value will be used instead.
+* `headers`: Custom HTTP headers, which are passed to Elasticsearch header
+  before each request.
 
 ## Known issues
 

plugins/outputs/elasticsearch/elasticsearch.go

@@ -47,6 +47,7 @@ type Elasticsearch struct {
 	Timeout             config.Duration   `toml:"timeout"`
 	URLs                []string          `toml:"urls"`
 	UsePipeline         string            `toml:"use_pipeline"`
+	Headers             map[string]string `toml:"headers"`
 	Log                 telegraf.Logger   `toml:"-"`
 	majorReleaseNumber  int
 	pipelineName        string
@@ -183,6 +184,16 @@ func (a *Elasticsearch) Connect() error {
 		elastic.SetGzip(a.EnableGzip),
 	)
 
+	if len(a.Headers) > 0 {
+		headers := http.Header{}
+		for k, vals := range a.Headers {
+			for _, v := range strings.Split(vals, ",") {
+				headers.Add(k, v)
+			}
+		}
+		clientOptions = append(clientOptions, elastic.SetHeaders(headers))
+	}
+
 	authOptions, err := a.getAuthOptions()
 	if err != nil {
 		return err

plugins/outputs/elasticsearch/sample.conf

@@ -77,3 +77,8 @@
   ## no pipeline is used for the metric.
   # use_pipeline = "{{es_pipeline}}"
   # default_pipeline = "my_pipeline"
+  #
+  # Custom HTTP headers
+  # To pass custom HTTP headers please define it in a given below section
+  # [outputs.elasticsearch.headers]
+  #    "X-Custom-Header" = "custom-value"