adding possibility to override content-type checks, it was breaking c…

…ertain webhooks that is not able to set content-headers at all. Still defaults to application/json (elastic#20232)

x-pack/filebeat/docs/inputs/input-http-endpoint.asciidoc

@@ -41,6 +41,17 @@ Custom response example:
   prefix: "json"
 ----
 
+Disable Content-Type checks
+["source","yaml",subs="attributes"]
+----
+{beatname_lc}.inputs:
+- type: http_endpoint
+  enabled: true
+  listen_address: 192.168.1.1
+  content_type: ""
+  prefix: "json"
+----
+
 Basic auth and SSL example:
 ["source","yaml",subs="attributes"]
 ----
@@ -80,6 +91,12 @@ If `basic_auth` is enabled, this is the username used for authentication against
 
 If `basic_auth` is eanbled, this is the password used for authentication against the HTTP listener. Requires `username` to also be set.
 
+[float]
+==== `content_type`
+
+By default the input expects the incoming POST to include a Content-Type of `application/json` to try to enforce the incoming data to be valid JSON.
+In certain scenarios when the source of the request is not able to do that, it can be overwritten with another value or set to null
+
 [float]
 ==== `response_code`
 

x-pack/filebeat/input/http_endpoint/config.go

@@ -23,6 +23,7 @@ type config struct {
 	ListenPort    string                  `config:"listen_port"`
 	URL           string                  `config:"url"`
 	Prefix        string                  `config:"prefix"`
+	ContentType   string                  `config:"content_type"`
 }
 
 func defaultConfig() config {
@@ -36,6 +37,7 @@ func defaultConfig() config {
 		ListenPort:    "8000",
 		URL:           "/",
 		Prefix:        "json",
+		ContentType:   "application/json",
 	}
 }
 

x-pack/filebeat/input/http_endpoint/input.go

@@ -87,7 +87,7 @@ func (e *httpEndpoint) Run(ctx v2.Context, publisher stateless.Publisher) error
 		username:    e.config.Username,
 		password:    e.config.Password,
 		method:      http.MethodPost,
-		contentType: "application/json",
+		contentType: e.config.ContentType,
 	}
 
 	handler := &httpHandler{