<s>
A	O
webhook	B-Protocol
in	O
web	O
development	O
is	O
a	O
method	O
of	O
augmenting	O
or	O
altering	O
the	O
behavior	O
of	O
a	O
web	O
page	O
or	O
web	B-Application
application	I-Application
with	O
custom	O
callbacks	O
.	O
</s>
<s>
The	O
term	O
"	O
webhook	B-Protocol
"	O
was	O
coined	O
by	O
Jeff	O
Lindsay	O
in	O
2007	O
from	O
the	O
computer	O
programming	O
term	O
hook	O
.	O
</s>
<s>
The	O
format	O
is	O
usually	O
JSON	B-General_Concept
.	O
</s>
<s>
The	O
request	O
is	O
done	O
as	O
a	O
HTTP	B-Protocol
POST	I-Protocol
request	I-Protocol
.	O
</s>
<s>
Webhooks	B-Protocol
are	O
"	O
user-defined	O
HTTP	O
callbacks	O
"	O
.	O
</s>
<s>
When	O
that	O
event	O
occurs	O
,	O
the	O
source	O
site	O
makes	O
an	O
HTTP	O
request	O
to	O
the	O
URL	O
configured	O
for	O
the	O
webhook	B-Protocol
.	O
</s>
<s>
Common	O
uses	O
are	O
to	O
trigger	O
builds	O
with	O
continuous	O
integration	O
systems	O
or	O
to	O
notify	O
bug	B-Application
tracking	I-Application
systems	I-Application
.	O
</s>
<s>
Because	O
webhooks	B-Protocol
use	O
HTTP	O
,	O
they	O
can	O
be	O
integrated	O
into	O
web	O
services	O
without	O
adding	O
new	O
infrastructure	O
.	O
</s>
<s>
When	O
the	O
client	O
(	O
the	O
originating	O
website	O
or	O
application	O
)	O
makes	O
a	O
webhook	B-Protocol
call	O
to	O
the	O
third-party	O
user	O
's	O
server	O
,	O
the	O
incoming	O
POST	B-Protocol
request	I-Protocol
should	O
be	O
authenticated	O
to	O
avoid	O
a	O
spoofing	O
attack	O
and	O
its	O
timestamp	O
verified	O
to	O
avoid	O
a	O
replay	O
attack	O
.	O
</s>
<s>
The	O
webhook	B-Protocol
can	O
include	O
information	O
about	O
what	O
type	O
of	O
event	O
it	O
is	O
,	O
and	O
a	O
shared	O
secret	O
or	O
digital	O
signature	O
to	O
verify	O
the	O
webhook	B-Protocol
.	O
</s>
<s>
An	O
HMAC	B-Algorithm
signature	O
can	O
be	O
included	O
as	O
a	O
HTTP	O
header	O
.	O
</s>
<s>
The	O
sender	O
may	O
choose	O
to	O
keep	O
a	O
constant	O
list	O
of	O
IP	B-Protocol
addresses	I-Protocol
from	O
which	O
requests	O
will	O
be	O
sent	O
.	O
</s>
