A
request header
is an
HTTP header
that can be used in an HTTP request to provide information about the request context, so that the server can tailor the response. For example, the
Accept-*
headers indicate the allowed and preferred formats of the response. Other headers can be used to supply authentication credentials (e.g.
Authorization
), to control caching, or to get information about the user agent or referrer, etc.
Not all headers that can appear in a request are referred to as
request headers
by the specification. For example, the
Content-Type
header is referred to as a
representation header
.
In addition,
CORS
defines a subset of request headers as
simple headers
, request headers that are always considered authorized and are not explicitly listed in responses to
preflight
requests.
The HTTP message below shows a few request headers after a
GET
request: