title: URLSession doesn't pass 'Authorization' key in header swift 4
body: <p>I am trying to pass authorization key in header of a URLRequest. But at the server end the key is not received. The same API when called from postman working fine. Any other key in the header is working fine, even authorizations key is visible at server end.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>let headers = [
      "authorization": "token abcd"
  ]
  
  var request = URLRequest.init(url: NSURL(string:
      "http://127.0.0.1:7000/api/channels?filter=contributed")! as URL)
  request.httpMethod = "GET"
  request.allHTTPHeaderFields = headers
  let config = URLSessionConfiguration.default
  config.httpAdditionalHeaders = headers
  let session = URLSession.init(configuration: config)
  
  let dataTask = session.dataTask(with: request, completionHandler: { (data, response, error) -&gt; Void in
      if (error != nil) {
          print(error ?? "")
      } else {
          let httpResponse = response as? HTTPURLResponse
          print(httpResponse ?? "")
      }
  })
  </code></pre>
  
  <p>As you can see, I tried to set the token in both session config and request but none is working. </p>