Can't asign content-type on POST

[megamauricio009]

Hi guys i'm trying to get a token from a service but it said's "error":"invalid_request","error_description":"Missing grant type
i was searching about this error and the solution is changing the content-type to "application/x-www-form-urlencoded" cause it can be sended by JSON. but it doesn't work, my code is this

`
var json = JSON.parse(JSON.stringify(jsonResp))

var body = decryptBody(req.body);
body = body.replace(/\0/g, '')
body = JSON.parse(body)
var auth = {grant_type:"password", username: "pass" , password: "usr" }
if(!isValidProtocol(body)){
//console.log(body)
json.error = true,
json.desc = 'invalid protocol'
res.statusCode = 202;
res.json(encryptBody(json));
}

requestify.request( "http://localhost:7070" + '/oauth/token',{
method: "POST",
headers: {'Content-Type': 'application/x-www-form-urlencoded'},
dataType: 'form-url-encoded',
auth: auth
})
.then(function(response) {
json.data = response.getBody();
res.json(encryptBody(json));
}).catch(function(err){
console.log('ERROR:')
console.log(err)
//console.log(body.data)
console.log(auth)
json.error = true,
json.desc = 'invalid login params'
res.statusCode = 202;
res.json(encryptBody(json));
});`

and the result

ERROR: Response { code: 400, headers: { 'x-content-type-options': 'nosniff', 'x-xss-protection': '1; mode=block', 'cache-control': 'no-cache, no-store, max-age=0, must-revalidate', pragma: 'no-cache', expires: '0', 'x-frame-options': 'DENY', 'content-type': 'application/json;charset=UTF-8', 'transfer-encoding': 'chunked', date: 'Tue, 20 Jun 2017 19:31:43 GMT', connection: 'close' }, body: '{"error":"invalid_request","error_description":"Missing grant type"}' }
Waitng for the answer, THANK YOU..