Swift - 8tracks.com API POST json data fails (422) everytime - objective-c

Question

I'm trying to talk with 8tracks open API in Swift iOS app. I need to make POST authorization request to http://8tracks.com/sessions.jsonwith AFNetworking but everytime I get 422 Unprocessable Entity error..
I tried this endpoint on the web and it works fine. Here is code that I'm using (subclassing AFHTTPSessionManager):
init() {
super.init()
self.responseSerializer = AFJSONResponseSerializer()
self.requestSerializer = AFJSONRequestSerializer()
self.requestSerializer.setValue(API_KEY, forHTTPHeaderField: "X-Api-Key")
self.requestSerializer.setValue("3", forHTTPHeaderField: "X-Api-Version")
}
func login(username: String, password: String, success: (NSURLSessionDataTask!, AnyObject!) -> Void, failure: ((NSURLSessionDataTask!, NSError!) -> Void)?) {
let credentials = ["username": username, "password": password] as Dictionary
self.POST(
API_URL.stringByAppendingString("/sessions.json"),
parameters: credentials,
success: success,
failure: failure
)
}
Error looks as follows:
{ URL: http://8tracks.com/sessions.json } { status code: 422, headers {
"Accept-Ranges" = bytes;
"Access-Control-Allow-Origin" = "*";
Age = 0;
"Cache-Control" = "max-age=0, private, must-revalidate";
Connection = "keep-alive";
"Content-Length" = 125;
"Content-Type" = "application/json; charset=utf-8";
Date = "Wed, 25 Jun 2014 19:29:12 GMT";
Server = "nginx/1.4.3";
Status = "422 Unprocessable Entity";
Via = "1.1 varnish";
"X-Action" = "sessions/create";
"X-Backend" = rails;
"X-Cache" = MISS;
"X-Data-Request" = 1;
"X-Request-Id" = 3040c8bf79936b27075731f634bfd534;
"X-Requests-Left" = 99;
"X-Runtime" = "0.257240";
"X-UA-Compatible" = "IE=Edge,chrome=1";
} }, NSLocalizedDescription=Request failed: client error (422),
NSErrorFailingURLKey=http://8tracks.com/sessions.json}

Answer 1

It might have something to do with subclass AFHTTPSessionManager without a baseURL. I've tested the following code and it works.
let path = "/sessions.json"
let params = ["login": login, "password": password, "api_version": "3"]
let success = {(task: NSURLSessionDataTask!, response: AnyObject!) -> Void in
println(response)
}
let failure = {(task: NSURLSessionDataTask!, error: NSError!) -> Void in
println(error)
}
var client = AFHTTPSessionManager(baseURL: NSURL(string: "https://8tracks.com"))
client.POST(path, parameters: params, success: success, failure: failure)