added "example using a custom HTTP Header field" to docu, issue https://github.com/composer/composer/issues/3756

doc/articles/handling-private-packages-with-satis.md

@@ -157,6 +157,26 @@ Example using HTTP over SSL using a client certificate:
 
 > **Tip:** See [ssl context options](http://www.php.net/manual/en/context.ssl.php) for more information.
 
+Example using a custom HTTP Header field for token authentication:
+
+```json
+{
+    "repositories": [
+        {
+            "type": "composer",
+            "url": "https://example.org",
+            "options":  {
+                "http": {
+                    "header": [
+                        "API-TOKEN: YOUR-API-TOKEN"
+                    ]
+                }
+            }
+        }
+    ]
+}
+```
+
 ### Authentification
 
 When your private repositories are password protected, you can store the authentification details permanently.