<s>
HTTP	B-Protocol
header	I-Protocol
fields	O
are	O
a	O
list	O
of	O
strings	O
sent	O
and	O
received	O
by	O
both	O
the	O
client	O
program	O
and	O
server	O
on	O
every	O
HTTP	O
request	O
and	O
response	O
.	O
</s>
<s>
These	O
headers	O
are	O
usually	O
invisible	O
to	O
the	O
end-user	O
and	O
are	O
only	O
processed	O
or	O
logged	B-Application
by	O
the	O
server	O
and	O
client	O
applications	O
.	O
</s>
<s>
They	O
define	O
how	O
information	O
sent/received	O
through	O
the	O
connection	O
are	O
encoded	O
(	O
as	O
in	O
Content-Encoding	O
)	O
,	O
the	O
session	O
verification	O
and	O
identification	O
of	O
the	O
client	O
(	O
as	O
in	O
browser	B-Application
cookies	I-Application
,	O
IP	O
address	O
,	O
user-agent	B-Protocol
)	O
or	O
their	O
anonymity	O
thereof	O
(	O
VPN	O
or	O
proxy	O
masking	O
,	O
user-agent	B-Protocol
spoofing	O
)	O
,	O
how	O
the	O
server	O
should	O
handle	O
data	O
(	O
as	O
in	O
Do-Not-Track	B-Protocol
)	O
,	O
the	O
age	O
(	O
the	O
time	O
it	O
has	O
resided	O
in	O
a	O
shared	O
cache	B-Protocol
)	O
of	O
the	O
document	O
being	O
downloaded	O
,	O
amongst	O
others	O
.	O
</s>
<s>
HTTP/2	B-Protocol
and	O
HTTP/3	B-Protocol
instead	O
use	O
a	O
binary	O
protocol	O
,	O
where	O
headers	O
are	O
encoded	O
in	O
a	O
single	O
HEADERS	O
and	O
zero	O
or	O
more	O
CONTINUATION	O
frames	O
using	O
HPACK	B-Protocol
(	O
HTTP/2	B-Protocol
)	O
or	O
QPACK	O
(	O
HTTP/3	B-Protocol
)	O
,	O
which	O
both	O
provide	O
efficient	O
header	O
compression	O
.	O
</s>
<s>
HTTP/2	B-Protocol
makes	O
some	O
restrictions	O
on	O
specific	O
header	O
fields	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
in	O
User-Agent	B-Protocol
,	O
Server	O
,	O
Via	O
fields	O
)	O
,	O
which	O
can	O
be	O
ignored	O
by	O
software	O
.	O
</s>
<s>
Many	O
field	O
values	O
may	O
contain	O
a	O
quality	O
(	O
q	O
)	O
key-value	O
pair	O
separated	O
by	O
equals	O
sign	O
,	O
specifying	O
a	O
weight	O
to	O
use	O
in	O
content	B-Protocol
negotiation	I-Protocol
.	O
</s>
<s>
See	O
Content	B-Protocol
negotiation	I-Protocol
.	O
</s>
<s>
See	O
HTTP	B-Protocol
compression	I-Protocol
.	O
</s>
<s>
Accept-Encoding	O
:	O
gzip	O
,	O
deflate	B-Algorithm
Permanent	O
Accept-Language	O
List	O
of	O
acceptable	O
human	O
languages	O
for	O
response	O
.	O
</s>
<s>
See	O
Content	B-Protocol
negotiation	I-Protocol
.	O
</s>
<s>
Accept-Language	O
:	O
en-US	O
Permanent	O
Initiates	O
a	O
request	O
for	O
cross-origin	B-General_Concept
resource	I-General_Concept
sharing	I-General_Concept
with	O
Origin	O
(	O
below	O
)	O
.	O
</s>
<s>
Access-Control-Request-Method	O
:	O
GET	O
Authorization	O
Authentication	O
credentials	O
for	O
HTTP	B-Protocol
authentication	I-Protocol
.	O
</s>
<s>
Authorization	O
:	O
Basic	O
QWxhZGRpbjpvcGVuIHNlc2FtZQ	O
==	O
Permanent	O
Cache-Control	O
Used	O
to	O
specify	O
directives	O
that	O
must	O
be	O
obeyed	O
by	O
all	O
caching	O
mechanisms	O
along	O
the	O
request-response	O
chain	O
.	O
</s>
<s>
Cache-Control	O
:	O
no-cache	O
Permanent	O
Connection	O
Control	O
options	O
for	O
the	O
current	O
connection	O
and	O
list	O
of	O
hop-by-hop	O
request	O
fields	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
with	O
HTTP/2	B-Protocol
.	O
</s>
<s>
Connection	B-Protocol
:	I-Protocol
Upgrade	I-Protocol
Permanent	O
Content-Encoding	O
The	O
type	O
of	O
encoding	O
used	O
on	O
the	O
data	O
.	O
</s>
<s>
See	O
HTTP	B-Protocol
compression	I-Protocol
.	O
</s>
<s>
Content-Length	O
:	O
348	O
Permanent	O
Content-MD5	O
A	O
Base64-encoded	O
binary	O
MD5	B-Algorithm
sum	O
of	O
the	O
content	O
of	O
the	O
request	O
body	O
.	O
</s>
<s>
Content-MD5	O
:	O
Q2hlY2sgSW50ZWdyaXR5IQ	O
==	O
Obsolete	O
Content-Type	B-Application
The	O
Media	B-Application
type	I-Application
of	O
the	O
body	O
of	O
the	O
request	O
(	O
used	O
with	O
POST	O
and	O
PUT	O
requests	O
)	O
.	O
</s>
<s>
Content-Type	B-Application
:	O
application/x	O
-www-form-urlencoded	O
Permanent	O
Cookie	B-Application
An	O
HTTP	B-Application
cookie	I-Application
previously	O
sent	O
by	O
the	O
server	O
with	O
Set-Cookie	O
(	O
below	O
)	O
.	O
</s>
<s>
Cookie	B-Application
:	O
$Version	O
=	O
1	O
;	O
Skin	O
=	O
new	O
;	O
Permanent	O
:	O
standard	O
Date	O
The	O
date	O
and	O
time	O
at	O
which	O
the	O
message	O
was	O
originated	O
(	O
in	O
"	O
HTTP-date	O
"	O
format	O
as	O
defined	O
by	O
RFC	O
9110	O
:	O
HTTP	O
Semantics	O
,	O
section	O
5.6.7	O
"	O
Date/Time	O
Formats	O
"	O
)	O
.	O
</s>
<s>
From	O
:	O
user@example.com	O
Permanent	O
Host	O
The	O
domain	O
name	O
of	O
the	O
server	O
(	O
for	O
virtual	O
hosting	O
)	O
,	O
and	O
the	O
TCP	B-Protocol
port	I-Protocol
number	O
on	O
which	O
the	O
server	O
is	O
listening	O
.	O
</s>
<s>
The	O
port	B-Protocol
number	I-Protocol
may	O
be	O
omitted	O
if	O
the	O
port	B-Protocol
is	O
the	O
standard	O
port	B-Protocol
for	O
the	O
service	O
requested	O
.	O
</s>
<s>
If	O
the	O
request	O
is	O
generated	O
directly	O
in	O
HTTP/2	B-Protocol
,	O
it	O
should	O
not	O
be	O
used	O
.	O
</s>
<s>
Host	O
:	O
en.wikipedia.orgHTTP2-SettingsA	O
request	O
that	O
upgrades	O
from	O
HTTP/1.1	O
to	O
HTTP/2	B-Protocol
MUST	O
include	O
exactly	O
one	O
HTTP2-Setting	O
header	O
field	O
.	O
</s>
<s>
The	O
HTTP2-Settings	O
header	O
field	O
is	O
a	O
connection-specific	O
header	O
field	O
that	O
includes	O
parameters	O
that	O
govern	O
the	O
HTTP/2	B-Protocol
connection	O
,	O
provided	O
in	O
anticipation	O
of	O
the	O
server	O
accepting	O
the	O
request	O
to	O
upgrade.HTTP2-Settings	O
:	O
token64Permanent	O
:	O
standard	O
If-Match	O
Only	O
perform	O
the	O
action	O
if	O
the	O
client	O
supplied	O
entity	O
matches	O
the	O
same	O
entity	O
on	O
the	O
server	O
.	O
</s>
<s>
If-Modified-Since	O
:	O
Sat	O
,	O
29	O
Oct	O
1994	O
19:43:31	O
GMT	O
Permanent	O
If-None-Match	O
Allows	O
a	O
304	O
Not	O
Modified	O
to	O
be	O
returned	O
if	O
content	O
is	O
unchanged	O
,	O
see	O
HTTP	B-Protocol
ETag	I-Protocol
.	O
</s>
<s>
Max-Forwards	O
:	O
10	O
Permanent	O
Origin	O
Initiates	O
a	O
request	O
for	O
cross-origin	B-General_Concept
resource	I-General_Concept
sharing	I-General_Concept
(	O
asks	O
server	O
for	O
Access-Control-*	O
response	O
fields	O
)	O
.	O
</s>
<s>
Pragma	O
:	O
no-cache	O
PermanentPreferAllows	O
client	O
to	O
request	O
that	O
certain	O
behaviors	O
be	O
employed	O
by	O
a	O
server	O
while	O
processing	O
a	O
request.Prefer	O
:	O
return	O
=	O
representationPermanentRFC	O
7240	O
Proxy-Authorization	O
Authorization	O
credentials	O
for	O
connecting	O
to	O
a	O
proxy	O
.	O
</s>
<s>
See	O
Byte	B-Protocol
serving	I-Protocol
.	O
</s>
<s>
Range	O
:	O
bytes	O
=	O
500-999	O
Permanent	O
Referer	B-Protocol
This	O
is	O
the	O
address	O
of	O
the	O
previous	O
web	O
page	O
from	O
which	O
a	O
link	O
to	O
the	O
currently	O
requested	O
page	O
was	O
followed	O
.	O
</s>
<s>
(	O
The	O
word	O
"	O
referrer	B-Protocol
"	O
has	O
been	O
misspelled	O
in	O
the	O
RFC	O
as	O
well	O
as	O
in	O
most	O
implementations	O
to	O
the	O
point	O
that	O
it	O
has	O
become	O
standard	O
usage	O
and	O
is	O
considered	O
correct	O
terminology	O
)	O
Referer	B-Protocol
:	O
http://en.wikipedia.org/wiki/Main_Page	O
Permanent	O
TE	O
The	O
transfer	O
encodings	O
the	O
user	B-Protocol
agent	I-Protocol
is	O
willing	O
to	O
accept	O
:	O
the	O
same	O
values	O
as	O
for	O
the	O
response	O
header	O
field	O
Transfer-Encoding	O
can	O
be	O
used	O
,	O
plus	O
the	O
"	O
trailers	O
"	O
value	O
(	O
related	O
to	O
the	O
"	O
chunked	B-Protocol
"	O
transfer	O
method	O
)	O
to	O
notify	O
the	O
server	O
it	O
expects	O
to	O
receive	O
additional	O
fields	O
in	O
the	O
trailer	O
after	O
the	O
last	O
,	O
zero-sized	O
,	O
chunk	O
.	O
</s>
<s>
Only	O
trailers	O
is	O
supported	O
in	O
HTTP/2	B-Protocol
.	O
</s>
<s>
TE	O
:	O
trailers	O
,	O
deflate	B-Algorithm
PermanentTrailerThe	O
Trailer	O
general	O
field	O
value	O
indicates	O
that	O
the	O
given	O
set	O
of	O
header	O
fields	O
is	O
present	O
in	O
the	O
trailer	O
of	O
a	O
message	O
encoded	O
with	O
chunked	O
transfer	O
coding.Trailer	O
:	O
Max-ForwardsPermanentTransfer-EncodingThe	O
form	O
of	O
encoding	O
used	O
to	O
safely	O
transfer	O
the	O
entity	O
to	O
the	O
user	O
.	O
</s>
<s>
Currently	O
defined	O
methods	O
are	O
:	O
chunked	B-Protocol
,	O
compress	O
,	O
deflate	B-Algorithm
,	O
gzip	O
,	O
identity	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
with	O
HTTP/2.Transfer	O
-Encoding	O
:	O
chunkedPermanent	O
User-Agent	B-Protocol
The	O
user	B-Protocol
agent	I-Protocol
string	O
of	O
the	O
user	B-Protocol
agent	I-Protocol
.	O
</s>
<s>
User-Agent	B-Protocol
:	O
Mozilla/5.0	O
(	O
X11	O
;	O
Linux	O
x86_64	O
;	O
rv:12.0	O
)	O
Gecko/20100101	O
Firefox/12.0	O
Permanent	O
Upgrade	B-Protocol
Ask	O
the	O
server	O
to	O
upgrade	B-Protocol
to	O
another	O
protocol	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
in	O
HTTP/2	B-Protocol
.	O
</s>
<s>
Upgrade	B-Protocol
:	O
h2c	O
,	O
HTTPS/1.3	O
,	O
IRC/6.9	O
,	O
RTA/x11	O
,	O
websocket	O
Permanent	O
Via	O
Informs	O
the	O
server	O
of	O
proxies	O
through	O
which	O
the	O
request	O
was	O
sent	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
with	O
HTTP/2	B-Protocol
Upgrade-Insecure-Requests	O
:	O
1	O
X-Requested-With	O
Mainly	O
used	O
to	O
identify	O
Ajax	B-General_Concept
requests	O
(	O
most	O
JavaScript	B-Application
frameworks	I-Application
send	O
this	O
field	O
with	O
value	O
of	O
XMLHttpRequest	O
)	O
;	O
also	O
identifies	O
Android	O
apps	O
using	O
WebView	O
X-Requested-With	O
:	O
XMLHttpRequest	O
DNT	B-Protocol
Requests	O
a	O
web	O
application	O
to	O
disable	O
their	O
tracking	O
of	O
a	O
user	O
.	O
</s>
<s>
This	O
is	O
Mozilla	O
's	O
version	O
of	O
the	O
X-Do-Not-Track	B-Protocol
header	O
field	O
(	O
since	O
Firefox	B-Application
4.0	I-Application
Beta	O
11	O
)	O
.	O
</s>
<s>
Safari	B-Application
and	O
IE9	B-Application
also	O
have	O
support	O
for	O
this	O
field	O
.	O
</s>
<s>
DNT	B-Protocol
:	O
0	O
(	O
Do	B-Protocol
Not	I-Protocol
Track	I-Protocol
Disabled	O
)	O
X-Forwarded-For	B-Protocol
A	O
de	O
facto	O
standard	O
for	O
identifying	O
the	O
originating	O
IP	O
address	O
of	O
a	O
client	O
connecting	O
to	O
a	O
web	O
server	O
through	O
an	O
HTTP	O
proxy	O
or	O
load	O
balancer	O
.	O
</s>
<s>
X-Forwarded-For	B-Protocol
:	O
129.78.138.66	O
,	O
129.78.64.103	O
X-Forwarded-Host	O
A	O
de	O
facto	O
standard	O
for	O
identifying	O
the	O
original	O
host	O
requested	O
by	O
the	O
client	O
in	O
the	O
Host	O
HTTP	O
request	O
header	O
,	O
since	O
the	O
host	O
name	O
and/or	O
port	B-Protocol
of	O
the	O
reverse	O
proxy	O
(	O
load	O
balancer	O
)	O
may	O
differ	O
from	O
the	O
origin	O
server	O
handling	O
the	O
request	O
.	O
</s>
<s>
This	O
can	O
be	O
used	O
when	O
a	O
user	B-Protocol
agent	I-Protocol
or	O
firewall	O
prevents	O
PUT	O
or	O
DELETE	O
methods	O
from	O
being	O
sent	O
directly	O
(	O
note	O
that	O
this	O
is	O
either	O
a	O
bug	O
in	O
the	O
software	O
component	O
,	O
which	O
ought	O
to	O
be	O
fixed	O
,	O
or	O
an	O
intentional	O
configuration	O
,	O
in	O
which	O
case	O
bypassing	O
it	O
may	O
be	O
the	O
wrong	O
thing	O
to	O
do	O
)	O
.	O
</s>
<s>
X-HTTP-Method-Override	O
:	O
DELETE	O
X-ATT-DeviceId	O
Allows	O
easier	O
parsing	O
of	O
the	O
MakeModel/Firmware	O
that	O
is	O
usually	O
found	O
in	O
the	O
User-Agent	B-Protocol
String	O
of	O
AT&T	O
Devices	O
X-Att-Deviceid	O
:	O
GT-P7320/P7320XXLPG	O
X-Wap-Profile	O
Links	O
to	O
an	O
XML	O
file	O
on	O
the	O
Internet	O
with	O
a	O
full	O
description	O
and	O
details	O
about	O
the	O
device	O
currently	O
connecting	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
with	O
HTTP/2	B-Protocol
.	O
</s>
<s>
Proxy-Connection	O
:	O
keep-alive	O
X-UIDH	O
Server-side	O
deep	B-Application
packet	I-Application
inspection	I-Application
of	O
a	O
unique	O
ID	O
identifying	O
customers	O
of	O
Verizon	B-Application
Wireless	I-Application
;	O
also	O
known	O
as	O
"	O
perma-cookie	O
"	O
or	O
"	O
supercookie	O
"	O
X-UIDH	O
:	O
...	O
X-Csrf-Token	O
Used	O
to	O
prevent	O
cross-site	B-Protocol
request	I-Protocol
forgery	I-Protocol
.	O
</s>
<s>
Alternative	O
header	O
names	O
are	O
:	O
X-CSRFToken	O
and	O
X-XSRF-TOKEN	O
X-Csrf-Token	O
:	O
i8XNjC4b8KVok4uw5RftR38Wgp2BFwqlX-Request-ID	O
,	O
</s>
<s>
Field	O
name	O
Description	O
Example	O
StatusStandard	O
Accept-CH	O
Requests	O
HTTP	B-Protocol
Client	I-Protocol
Hints	I-Protocol
Accept-CH	O
:	O
UA	O
,	O
Platform	O
Experimental	O
Specifying	O
which	O
web	O
sites	O
can	O
participate	O
in	O
cross-origin	B-General_Concept
resource	I-General_Concept
sharing	I-General_Concept
Access-Control-Allow-Origin	B-General_Concept
:	O
*	O
Accept-Patch	O
Specifies	O
which	O
patch	O
document	O
formats	O
this	O
server	O
supports	O
Accept-Patch	O
:	O
text/example	O
;	O
charset	O
=	O
utf-8	O
Permanent	O
Accept-Ranges	O
What	O
partial	O
content	O
range	O
types	O
this	O
server	O
supports	O
via	O
byte	B-Protocol
serving	I-Protocol
Accept-Ranges	O
:	O
bytes	O
Permanent	O
Age	O
The	O
age	O
the	O
object	O
has	O
been	O
in	O
a	O
proxy	B-Protocol
cache	I-Protocol
in	O
seconds	O
Age	O
:	O
12	O
Permanent	O
Allow	O
Valid	O
methods	O
for	O
a	O
specified	O
resource	O
.	O
</s>
<s>
When	O
using	O
HTTP/2	B-Protocol
,	O
servers	O
should	O
instead	O
send	O
an	O
ALTSVC	O
frame	O
.	O
</s>
<s>
Alt-Svc	O
:	O
http/1.1	O
=	O
"	O
http2.example.com:8001	O
"	O
;	O
ma	O
=	O
7200	O
Permanent	O
Cache-Control	O
Tells	O
all	O
caching	O
mechanisms	O
from	O
server	O
to	O
client	O
whether	O
they	O
may	O
cache	B-Protocol
this	O
object	O
.	O
</s>
<s>
It	O
is	O
measured	O
in	O
seconds	O
Cache-Control	O
:	O
max-age	O
=	O
3600	O
Permanent	O
Connection	O
Control	O
options	O
for	O
the	O
current	O
connection	O
and	O
list	O
of	O
hop-by-hop	O
response	O
fields	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
with	O
HTTP/2	B-Protocol
.	O
</s>
<s>
Connection	O
:	O
close	O
Permanent	O
Content-Disposition	O
An	O
opportunity	O
to	O
raise	O
a	O
"	O
File	O
Download	O
"	O
dialogue	O
box	O
for	O
a	O
known	O
MIME	B-Application
type	I-Application
with	O
binary	O
format	O
or	O
suggest	O
a	O
filename	O
for	O
dynamic	O
content	O
.	O
</s>
<s>
See	O
HTTP	B-Protocol
compression	I-Protocol
.	O
</s>
<s>
Content-Encoding	O
:	O
gzip	O
Permanent	O
Content-Language	O
The	O
natural	O
language	O
or	O
languages	O
of	O
the	O
intended	O
audience	O
for	O
the	O
enclosed	O
content	O
Content-Language	O
:	O
da	O
Permanent	O
Content-Length	O
The	O
length	O
of	O
the	O
response	O
body	O
in	O
octets	O
(	O
8-bit	O
bytes	O
)	O
Content-Length	O
:	O
348	O
Permanent	O
Content-Location	O
An	O
alternate	O
location	B-Protocol
for	O
the	O
returned	O
data	O
Content-Location	O
:	O
/index.htm	O
Permanent	O
Content-MD5	O
A	O
Base64-encoded	O
binary	O
MD5	B-Algorithm
sum	O
of	O
the	O
content	O
of	O
the	O
response	O
Content-MD5	O
:	O
Q2hlY2sgSW50ZWdyaXR5IQ	O
==	O
Obsolete	O
Content-Range	O
Where	O
in	O
a	O
full	O
body	O
message	O
this	O
partial	O
message	O
belongs	O
Content-Range	O
:	O
bytes	O
21010-47021/47022	O
Permanent	O
Content-Type	B-Application
The	O
MIME	B-Application
type	I-Application
of	O
this	O
content	O
Content-Type	B-Application
:	O
text/html	O
;	O
charset	O
=	O
utf-8	O
Permanent	O
Date	O
The	O
date	O
and	O
time	O
that	O
the	O
message	O
was	O
sent	O
(	O
in	O
"	O
HTTP-date	O
"	O
format	O
as	O
defined	O
by	O
RFC	O
9110	O
)	O
Date	O
:	O
Tue	O
,	O
15	O
Nov	O
1994	O
08:12:31	O
GMT	O
Permanent	O
Delta-Base	O
Specifies	O
the	O
delta-encoding	O
entity	B-Protocol
tag	I-Protocol
of	O
the	O
response	O
.	O
</s>
<s>
Delta-Base	O
:	O
"	O
abc	O
"	O
Permanent	O
ETag	B-Protocol
An	O
identifier	O
for	O
a	O
specific	O
version	O
of	O
a	O
resource	O
,	O
often	O
a	O
message	B-Algorithm
digest	I-Algorithm
ETag	B-Protocol
:	O
"	O
737060cd8c284d8af7ad3082f209582d	O
"	O
Permanent	O
Expires	O
Gives	O
the	O
date/time	O
after	O
which	O
the	O
response	O
is	O
considered	O
stale	O
(	O
in	O
"	O
HTTP-date	O
"	O
format	O
as	O
defined	O
by	O
RFC	O
9110	O
)	O
Expires	O
:	O
Thu	O
,	O
01	O
Dec	O
1994	O
16:00:00	O
GMT	O
Permanent	O
:	O
standard	O
IM	O
Instance-manipulations	O
applied	O
to	O
the	O
response	O
.	O
</s>
<s>
IM	O
:	O
feed	O
Permanent	O
Last-Modified	O
The	O
last	O
modified	O
date	O
for	O
the	O
requested	O
object	O
(	O
in	O
"	O
HTTP-date	O
"	O
format	O
as	O
defined	O
by	O
RFC	O
9110	O
)	O
Last-Modified	O
:	O
Tue	O
,	O
15	O
Nov	O
1994	O
12:45:26	O
GMT	O
Permanent	O
Link	O
Used	O
to	O
express	O
a	O
typed	O
relationship	O
with	O
another	O
resource	O
,	O
where	O
the	O
relation	O
type	O
is	O
defined	O
by	O
RFC	O
5988	O
Link	O
:	O
</feed>	O
;	O
rel	O
=	O
"	O
alternate	O
"	O
Indicate	O
the	O
canonical	O
version	O
of	O
a	O
URL	O
by	O
responding	O
with	O
the	O
Link	O
rel	O
=	O
"	O
canonical	O
"	O
HTTP	B-Protocol
header	I-Protocol
Retrieved	O
:	O
2012-02-09	O
Permanent	O
Location	B-Protocol
Used	O
in	O
redirection	O
,	O
or	O
when	O
a	O
new	O
resource	O
has	O
been	O
created	O
.	O
</s>
<s>
Example	O
2	O
:	O
Location	B-Protocol
:	O
/pub/WWW/People.html	O
PermanentP3P	O
This	O
field	O
is	O
supposed	O
to	O
set	O
P3P	O
policy	O
,	O
in	O
the	O
form	O
of	O
P3P:CP	O
=	O
"	O
your_compact_policy	O
"	O
.	O
</s>
<s>
However	O
,	O
P3P	O
did	O
not	O
take	O
off	O
,	O
W3C	O
P3P	O
Work	O
Suspended	O
most	O
browsers	O
have	O
never	O
fully	O
implemented	O
it	O
,	O
a	O
lot	O
of	O
websites	O
set	O
this	O
field	O
with	O
fake	O
policy	O
text	O
,	O
that	O
was	O
enough	O
to	O
fool	O
browsers	O
the	O
existence	O
of	O
P3P	O
policy	O
and	O
grant	O
permissions	O
for	O
third	O
party	O
cookies	B-Application
.	O
</s>
<s>
Pragma	O
:	O
no-cache	O
PermanentPreference-AppliedIndicates	O
which	O
Prefer	O
tokens	O
were	O
honored	O
by	O
the	O
server	O
and	O
applied	O
to	O
the	O
processing	O
of	O
the	O
request.Preference-Applied	O
:	O
return	O
=	O
representationPermanentRFC	O
7240	O
Proxy-Authenticate	O
Request	O
authentication	O
to	O
access	O
the	O
proxy	O
.	O
</s>
<s>
Proxy-Authenticate	O
:	O
Basic	O
Permanent	O
Public-Key-Pins	B-Protocol
HTTP	B-Protocol
Public	I-Protocol
Key	I-Protocol
Pinning	I-Protocol
,	O
announces	O
hash	B-Algorithm
of	O
website	O
's	O
authentic	O
TLS	B-Protocol
certificate	O
Public-Key-Pins	B-Protocol
:	O
max-age	O
=	O
2592000	O
;	O
pin-sha256	O
=	O
"	O
E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g	O
=	O
"	O
;	O
Permanent	O
Retry-After	O
If	O
an	O
entity	O
is	O
temporarily	O
unavailable	O
,	O
this	O
instructs	O
the	O
client	O
to	O
try	O
again	O
later	O
.	O
</s>
<s>
Example	O
2	O
:	O
Retry-After	O
:	O
Fri	O
,	O
07	O
Nov	O
2014	O
23:59:59	O
GMTPermanent	O
Server	O
A	O
name	O
for	O
the	O
server	O
Server	O
:	O
Apache/2.4.1	O
(	O
Unix	O
)	O
Permanent	O
Set-Cookie	O
An	O
HTTP	B-Application
cookie	I-Application
Set-Cookie	O
:	O
UserID	O
=	O
JohnDoe	O
;	O
Max-Age	O
=	O
3600	O
;	O
Version	O
=	O
1	O
Permanent	O
:	O
standard	O
Strict-Transport-Security	B-Protocol
A	O
HSTS	O
Policy	O
informing	O
the	O
HTTP	O
client	O
how	O
long	O
to	O
cache	B-Protocol
the	O
HTTPS	O
only	O
policy	O
and	O
whether	O
this	O
applies	O
to	O
subdomains	O
.	O
</s>
<s>
Strict-Transport-Security	B-Protocol
:	O
max-age	O
=	O
16070400	O
;	O
includeSubDomains	O
Permanent	O
:	O
standard	O
Trailer	O
The	O
Trailer	O
general	O
field	O
value	O
indicates	O
that	O
the	O
given	O
set	O
of	O
header	O
fields	O
is	O
present	O
in	O
the	O
trailer	O
of	O
a	O
message	O
encoded	O
with	O
chunked	B-Protocol
transfer	I-Protocol
coding	I-Protocol
.	O
</s>
<s>
Currently	O
defined	O
methods	O
are	O
:	O
chunked	B-Protocol
,	O
compress	O
,	O
deflate	B-Algorithm
,	O
gzip	O
,	O
identity	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
with	O
HTTP/2	B-Protocol
.	O
</s>
<s>
Transfer-Encoding	O
:	O
chunked	B-Protocol
PermanentTkTracking	O
Status	B-Protocol
header	O
,	O
value	O
suggested	O
to	O
be	O
sent	O
in	O
response	O
to	O
a	O
DNT(do-not-track )	O
,	O
possible	O
values	O
:	O
</s>
<s>
"	O
U	O
"	O
—	O
updatedTk	O
:	O
?	O
Permanent	O
Upgrade	B-Protocol
Ask	O
the	O
client	O
to	O
upgrade	B-Protocol
to	O
another	O
protocol	O
.	O
</s>
<s>
Must	O
not	O
be	O
used	O
in	O
HTTP/2	B-Protocol
Upgrade	B-Protocol
:	O
h2c	O
,	O
HTTPS/1.3	O
,	O
IRC/6.9	O
,	O
RTA/x11	O
,	O
websocket	O
Permanent	O
Vary	O
Tells	O
downstream	O
proxies	O
how	O
to	O
match	O
future	O
request	O
headers	O
to	O
decide	O
whether	O
the	O
cached	O
response	O
can	O
be	O
used	O
rather	O
than	O
requesting	O
a	O
fresh	O
one	O
from	O
the	O
origin	O
server	O
.	O
</s>
<s>
Field	O
name	O
Description	O
Example	O
Content-Security-Policy	O
,	O
X-Content-Security-Policy	O
,	O
X-WebKit-CSPContent	O
Security	O
Policy	O
definition.X-WebKit-CSP	O
:	O
default-src	O
'	O
self	O
 '	O
Expect-CT	O
Notify	O
to	O
prefer	O
to	O
enforce	O
Certificate	O
Transparency.Expect-CT	O
:	O
max-age	O
=	O
604800	O
,	O
enforce	O
,	O
report-uri	O
=	O
"	O
https://example.example/report	O
"	O
NEL	O
Used	O
to	O
configure	O
network	O
request	O
logging	B-Application
.	O
</s>
<s>
Permissions-Policy	O
:	O
fullscreen	O
=(	O
)	O
,	O
camera	O
=(	O
)	O
,	O
microphone	O
=(	O
)	O
,	O
geolocation	O
=(	O
)	O
,	O
interest-cohort	O
=(	O
)	O
Refresh	B-Protocol
Used	O
in	O
redirection	O
,	O
or	O
when	O
a	O
new	O
resource	O
has	O
been	O
created	O
.	O
</s>
<s>
This	O
refresh	B-Protocol
redirects	O
after	O
5	O
seconds	O
.	O
</s>
<s>
Defined	O
by	O
HTML	O
Standard	O
Refresh	B-Protocol
:	O
5	O
;	O
url	O
=	O
http://www.w3.org/pub/WWW/People.html	O
Report-To	O
Instructs	O
the	O
user	B-Protocol
agent	I-Protocol
to	O
store	O
reporting	O
endpoints	O
for	O
an	O
origin	O
.	O
</s>
<s>
Status	B-Protocol
CGI	B-Language
header	O
field	O
specifying	O
the	O
status	B-Protocol
of	O
the	O
HTTP	O
response	O
.	O
</s>
<s>
Timing-Allow-Origin	O
:	O
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1 ]*	O
X-Content-Duration	O
Provide	O
the	O
duration	O
of	O
the	O
audio	O
or	O
video	O
in	O
seconds	O
;	O
only	O
supported	O
by	O
Gecko	O
browsers	O
X-Content-Duration	O
:	O
42.666	O
X-Content-Type-Options	O
The	O
only	O
defined	O
value	O
,	O
"	O
nosniff	O
"	O
,	O
prevents	O
Internet	B-Application
Explorer	I-Application
from	O
MIME-sniffing	O
a	O
response	O
away	O
from	O
the	O
declared	O
content-type	B-Application
.	O
</s>
<s>
This	O
also	O
applies	O
to	O
Google	B-Application
Chrome	I-Application
,	O
when	O
downloading	O
extensions	O
.	O
</s>
<s>
X-Content-Type-Options	O
:	O
nosniff	O
X-Powered-By	O
Specifies	O
the	O
technology	O
(	O
e.g.	O
</s>
<s>
Also	O
used	O
to	O
activate	O
Chrome	B-Operating_System
Frame	I-Operating_System
in	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
If	O
a	O
web	O
server	O
responds	O
with	O
Cache-Control	O
:	O
no-cache	O
then	O
a	O
web	O
browser	O
or	O
other	O
caching	B-Protocol
system	I-Protocol
(	O
intermediate	O
proxies	O
)	O
must	O
not	O
use	O
the	O
response	O
to	O
satisfy	O
subsequent	O
requests	O
without	O
first	O
checking	O
with	O
the	O
originating	O
server	O
(	O
this	O
process	O
is	O
called	O
validation	O
)	O
.	O
</s>
<s>
Notice	O
that	O
no-cache	O
is	O
not	O
instructing	O
the	O
browser	O
or	O
proxies	O
about	O
whether	O
or	O
not	O
to	O
cache	B-Protocol
the	O
content	O
.	O
</s>
<s>
It	O
just	O
tells	O
the	O
browser	O
and	O
proxies	O
to	O
validate	O
the	O
cache	B-Protocol
content	O
with	O
the	O
server	O
before	O
using	O
it	O
(	O
this	O
is	O
done	O
by	O
using	O
If-Modified-Since	O
,	O
If-Unmodified-Since	O
,	O
If-Match	O
,	O
If-None-Match	O
attributes	O
mentioned	O
above	O
)	O
.	O
</s>
<s>
Sending	O
a	O
no-cache	O
value	O
thus	O
instructs	O
a	O
browser	O
or	O
proxy	O
to	O
not	O
use	O
the	O
cache	B-Protocol
contents	O
merely	O
based	O
on	O
"	O
freshness	O
criteria	O
"	O
of	O
the	O
cache	B-Protocol
content	O
.	O
</s>
<s>
Another	O
common	O
way	O
to	O
prevent	O
old	O
content	O
from	O
being	O
shown	O
to	O
the	O
user	O
without	O
validation	O
is	O
Cache-Control	O
:	O
max-age	O
=	O
0	O
.	O
</s>
<s>
This	O
instructs	O
the	O
user	B-Protocol
agent	I-Protocol
that	O
the	O
content	O
is	O
stale	O
and	O
should	O
be	O
validated	O
before	O
use	O
.	O
</s>
<s>
The	O
header	O
field	O
Cache-Control	O
:	O
no-store	O
is	O
intended	O
to	O
instruct	O
a	O
browser	O
application	O
to	O
make	O
a	O
best	O
effort	O
not	O
to	O
write	O
it	O
to	O
disk	O
(	O
i.e	O
not	O
to	O
cache	B-Protocol
it	O
)	O
.	O
</s>
<s>
Many	O
user	B-Protocol
agents	I-Protocol
show	O
different	O
behavior	O
in	O
loading	O
pages	O
from	O
the	O
history	O
store	O
or	O
cache	B-Protocol
depending	O
on	O
whether	O
the	O
protocol	O
is	O
HTTP	O
or	O
HTTPS	O
.	O
</s>
<s>
The	O
Cache-Control	O
:	O
no-cache	O
HTTP/1.1	O
header	O
field	O
is	O
also	O
intended	O
for	O
use	O
in	O
requests	O
made	O
by	O
the	O
client	O
.	O
</s>
<s>
The	O
Pragma	O
:	O
no-cache	O
header	O
field	O
,	O
defined	O
in	O
the	O
HTTP/1.0	O
spec	O
,	O
has	O
the	O
same	O
purpose	O
.	O
</s>
<s>
The	O
behavior	O
of	O
Pragma	O
:	O
no-cache	O
in	O
a	O
response	O
is	O
implementation	O
specific	O
.	O
</s>
<s>
While	O
some	O
user	B-Protocol
agents	I-Protocol
do	O
pay	O
attention	O
to	O
this	O
field	O
in	O
responses	O
,	O
the	O
HTTP/1.1	O
RFC	O
specifically	O
warns	O
against	O
relying	O
on	O
this	O
behavior	O
.	O
</s>
