title: Can't setRequestProperty key to "Authorization", but any other key value will work
body: <p>I was trying to quickly go over Java by coding a quick and simple oauth2 connection for Twitter, but I've encountered this really strange behaviour when trying to setRequestProperty to request headers.</p>
  
  <p>For instance, if I run the following code to add a request header called "Authorization":</p>
  
  <pre><code>connection.setRequestProperty("Authorization", b64Keys);
  </code></pre>
  
  <p>My request headers will prints as such and the "Authorization" header will be missing:</p>
  
  <blockquote>
    <p>{grant_type=[client_credentials],
    Content-Type=[application/x-www-form-urlencoded;charset=UTF-8]}</p>
  </blockquote>
  
  <p>But if I change the name of the key to "Authorizations" or "test" (or anything else), the setRequestPropert function actually adds the header. Doing so will result in the following output:</p>
  
  <blockquote>
    <p>{Authorizations=[Basic
    WVE0UzNJcmVKUEMYSECRETBASE64CODE2MxWkRNcnNiMg==],
    grant_type=[client_credentials],
    Content-Type=[application/x-www-form-urlencoded;charset=UTF-8]}</p>
  </blockquote>
  
  <p>Here is the full method:</p>
  
  <pre><code>    public String createRequest() throws IOException {
          String tokenBaseURL = "https://api.twitter.com/oauth2/token",publicKey= "",privateKey = "";
          String charset = "UTF-8";
          privateKey = "PRIVATEKEY";
          publicKey = "PUBLICKEY";
  
          String keyString = publicKey + ":" + privateKey;
          String b64Keys = "Basic "+Base64.getEncoder().encodeToString(keyString.getBytes());
          System.out.println(b64Keys);
  
          URL url = new URL(tokenBaseURL);
          HttpsURLConnection connection = (HttpsURLConnection)url.openConnection();
  
  
          connection.setRequestMethod("POST");
          connection.setRequestProperty("Authorization", b64Keys);
          connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");
          connection.setRequestProperty("grant_type","client_credentials");
          System.out.println(connection.getRequestProperties().toString());
  
          connection.setDoOutput(true); // Triggers xsPOST.
  
          return connection.getContent().toString();
  
      }
  </code></pre>
  
  <p>Is there something I am missing or is this possibly a bug? I need to be able to add a request header with a key named "Authorization"</p>