Calling an API with HTTP Header and Body with Alamofire - swift

Question

I'm trying to recreate a POST request that already works in Postman in Swift 3 with Alamofire 4, but i'm always getting a Status Code 400 "Bad Request". I am out of ideas about what I'm doing wrong here.
This is the request in Postman, additionally there is a username and password in the Body in JSON format:
Reading the Docs for Alamofire, I thought this should be the correct Swift code:
func login(as username: String, withPassword password: String) {
let url = "https://api2.drive-now.com/login"
let parameters: Parameters = [
"username" : username,
"password" : password
]
let loginHeaders: HTTPHeaders = [
"Accept" : "application/json;v=1.6",
"Accept-Encoding" : "gzip, deflate, sdch",
"Accept-Language" : "de-DE,de;q=0.8,en-US;q=0.6,en;q=0.4",
"Connection" : "keep-alive",
"Host" : "api2.drive-now.com",
"Origin" : "https://de.drive-now.com",
"X-Api-Key" : "adf51226795afbc4e7575ccc124face7",
"X-Language" : "de",
"Content-Type" : "application/json"
]
Alamofire.request(url, method: .post, parameters: parameters, encoding: JSONEncoding.default, headers: loginHeaders).responseJSON { response in
print("Request: \(response.request)") // original URL request
print("Response: \(response.response)") // HTTP URL response
print("Data: \(response.data)") // server data
print("Result: \(response.result)") // result of response serialization
if let JSON = response.result.value {
print("JSON: \(JSON)")
}
}
}
My console output is:
Request: Optional(https://api2.drive-now.com/login)
Response: Optional(<NSHTTPURLResponse: 0x6000000266a0> { URL: https://api2.drive-now.com/login } { status code: 400, headers {
Connection = close;
"Content-Length" = 181;
"Content-Type" = "text/html";
Date = "Tue, 13 Dec 2016 22:12:46 GMT";
Server = "nginx/1.4.6 (Ubuntu)";
} })
Data: Optional(181 bytes)
Result: FAILURE
Is there a custom session manager maybe that I have to implement? Or do you know of any debugging methods I could use here?

Answer 1

A friend accustomed to the API did help me resolve the issue: it was a default header field that seems to be added by Alamofire to every call. The API didn't accept calls with a "User-Agent" set (don't ask me why).
To help others who might have the same problem, I share the steps I went through to find and resolve the issue:
I made Alamofire.request(...) into a variable named postage (you can call it however you like, of course)
I added debugPrint(postage) to the end of the login-function
The output showed the additional header field
I constructed a custom SessionManager like below
var headers = Alamofire.SessionManager.defaultHTTPHeaders
headers.removeValue(forKey: "User-Agent")
let configuration = URLSessionConfiguration.default
configuration.httpAdditionalHeaders = headers
api = Alamofire.SessionManager(configuration: configuration)