DECLARE @Object AS INT;
DECLARE @ResponseText AS VARCHAR(8000);
DECLARE @Body AS VARCHAR(8000) = 
'{
    "what": 1,
    "ever": "you",
    "need": "to send as the body"
}'  

EXEC sp_OACreate 'MSXML2.XMLHTTP', @Object OUT;
EXEC sp_OAMethod @Object, 'open', NULL, 'post','http://requestb.in/1h83e3n1', 'false'

EXEC sp_OAMethod @Object, 'setRequestHeader', null, 'Content-Type', 'application/json'
EXEC sp_OAMethod @Object, 'send', null, @body

EXEC sp_OAMethod @Object, 'responseText', @ResponseText OUTPUT
SELECT @ResponseText

EXEC sp_OADestroy @Object