A header is part of the Data Connector Resource's interaction with a data source's endpoint that contains metadata regarding that interaction. A header is included when a Resource makes a request to (contacts) the data source endpoint; likewise, the endpoint includes a response header that is included when that endpoint responds to that request. Headers are used to provide information to both the Data Connector and the data source. Headers can be used for many purposes, including authentication and providing information about the body content of the request/response.