Making a POST request to Google OAuth using WWWForms

Hi, I'm trying to write a WWWForm to make a HTTP POST request to exchange an auth code for an access token. This is my first time working with WWWForms and I would like a bit of guidance.

Google gives an example of the request:

 POST /oauth2/v4/token HTTP/1.1
 Host: www.googleapis.com
 Content-Type: application/x-www-form-urlencoded
 
 code=4/v6xr77ewYqhvHSyW6UJ1w7jKwAzu&
 client_id=8819981768.apps.googleusercontent.com&
 client_secret=your_client_secret&
 redirect_uri=https://oauth2.example.com/code&
 grant_type=authorization_code

I retrieve my auth code using GetServerAuthCode(), and pass that to this function:

         public IEnumerator GetGoogleAccessToken(string auth_code) {
             WWWForm form = new WWWForm();
     
             Dictionary<string, string> headers = new Dictionary<string, string>();
    
             headers.Add("Host", "www.googleapis.com");
             headers.Add("Content-Type", "application/x-www-form-urlencoded");
             form.AddField("code", auth_code + "&");
             form.AddField("client_id", client_id);
             form.AddField("client_secret", client_secret);
             form.AddField ("redirect_uri", redirect_uri);
             form.AddField("grant_type", "authorization_code");
             byte[] rawData = form.data;
 
             WWW www = new WWW(token_uri, rawData, headers);
             yield return www;
         }

1. Am I suppose to append '&' to the end of all my strings?

2. Referring to this, section 4: https://developers.google.com/identity/protocols/OpenIDConnect I believe that my endpoint url should be https://www.googleapis.com/oauth2/v4/token ? Does that seem correct?

3. Why is it that when I do not modify headers, I can call WWW(url, form), but when I do, I have to call WWW(url, rawData, headers) ? In other words, how does sending a form differ from sending a byte array?

4. I'm expecting JSON data to be return. Any examples or suggestions on how I should parse that in C#?

Thank you!