Spotify API Authorization Error (Swift) - ios

Question

I've made a little App in Swift where a user can search the Spotify database for songs. I am using the Web API Console > Search for an Item. My problem is the new OAuth system where you have to sign-in and all that stuff. My authorization is ok, but when I'm trying to get an access token with the following code, it's returning me the following error: {"error":"server_error","error_description":"Unexpected status: 400"}. My code is:
let keys = "<MY_APPLICATION_KEYS>"
let url = NSURL(string: "https://accounts.spotify.com/api/token")
let session = URLSession.shared
let request = NSMutableURLRequest(url: url! as URL)
request.httpMethod = "POST"
request.setValue("Basic \(keys)", forHTTPHeaderField: "Authorization")
request.setValue("client_credentials", forHTTPHeaderField: "grant_type")
let task = session.dataTask(with: request as URLRequest) { (data, response, error) in
guard let _: Data = data, let _: URLResponse = response, error == nil else {
print(error!)
return
}
let dataString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)
print("Data: \(dataString!)")
self.parseData(JSONData: data!)
}
task.resume()
}
var accessToken = ""
func parseData(JSONData : Data) {
do {
var readableJSON = try JSONSerialization.jsonObject(with: JSONData, options: .mutableContainers) as! JSONStandard
if let token = readableJSON["access_token"] as? String {
accessToken = token
}
print("Access Token: \(accessToken)")
updateTokenInFirebase()
}
catch{
print(error)
}
Any help would be very appreciated, thank you very much in advance!
Documentation of the Web API: Web API Link
I am using on the Client Credentials Flow the first method.

Answer 1

I know it's been ~1 year since you posted this but I had the same issue and after a few tries was able to get it. You can test this in Playground.
import Foundation
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
if let url = URL(string: "https://accounts.spotify.com/api/token") {
var postRequest = URLRequest(url: url)
postRequest.httpMethod = "POST"
let bodyParams = "grant_type=client_credentials"
postRequest.httpBody = bodyParams.data(using: String.Encoding.ascii, allowLossyConversion: true)
let id = "your client id"
let secret = "your secret"
let combined = "\(id):\(secret)"
let combo = "\(id):\(secret)".toBase64()
postRequest.addValue("Basic \(combo)", forHTTPHeaderField: "Authorization")
let task = URLSession.shared.dataTask(with: postRequest) { (data, response, error) in
guard let data = data else {
return
}
print(String(data: data, encoding: String.Encoding.utf8)!)
}
task.resume()
}
extension String {
func fromBase64() -> String? {
guard let data = Data(base64Encoded: self) else {
return nil
}
return String(data: data, encoding: .utf8)
}
func toBase64() -> String {
return Data(self.utf8).base64EncodedString()
}
}

Answer 2

I know this is really late, but the issue is with this line:
request.setValue("client_credentials", forHTTPHeaderField: "grant_type")
According to the authorization guide, this should be in the body of the request, not the headers.