Twitter OAuth Flow - Confused about oob/3-legged a

Continuation from : Setting up Twitter OAuth without 3rd party libraries

Thanks to Mr. Nylander's help, I managed to get my oAuth class working (albeit only after a long time)! However, I'm confused about a few aspects of the oAuth flow.

Here's a breakdown of what's happening in a program I made:

==edit, I think I'll post partial code, it's hard to explain with just words for me==

//1st code segment
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://api.twitter.com/oauth/request_token");
string response = "";
HttpWebResponse resp = (HttpWebResponse)request.GetResponse();
using (StreamReader reader = new StreamReader(resp.GetResponseStream()))
{
response = reader.ReadToEnd();
}

Up to this point, I can get the response successfully.

Response --> oauth_token=asjndiqufh9uf&oauth_token_secret=oinroiqurhwunwer&oauth_callback_confirmed=true

//2nd code segment
Process proc = new Process();
proc.StartInfo.UseShellExecute = true;
proc.StartInfo.FileName = "https://api.twitter.com/oauth/authenticate?" + response;
proc.Start();

This brings the user(me) to a page where I have to choose whether I want to authorize it or not. If I agree, I'll then be taken to a page which contains a PIN.

//3rd code segment
Console.WriteLine("Enter the PIN");
string pin = Console.ReadLine();
baseString = generateBaseString("POST", "https://api.twitter.com/oauth/access_token", oauth_token);
oauth_signature = generateSignature(baseString, oauth_token_secret);

HttpWebRequest request2 = (HttpWebRequest)WebRequest.Create("https://api.twitter.com/oauth/access_token");
request2.Method = "POST";
request2.Headers["Authorization"] = generateAuthorizationHeader(oauth_token);
string response2 = "";
HttpWebResponse resp2 = (HttpWebResponse)request2.GetResponse();
using (StreamReader reader = new StreamReader(resp2.GetResponseStream()))
{
response2 = reader.ReadToEnd();
}
        Console.WriteLine(response2);

    }

The code here just requests for the PIN to be entered into the application and then returns the final oauth_token and oauth_token_secret in response2 for a fully working oAuth app. (tl;dr - At this point, the app already has ALL the tokens it needs)

-If I have NOT logged in during the second code segment, regardless of wether I enter a PIN or not, I get a 401 Unauthorized error, I'm guessing this is expected.

-If I have logged in during the second code segment and have been directed to the PIN page, but then chose NOT to enter the PIN/enter some wrong PIN into my application, I still get successfully authenticated and can get the final tokens without any problems. Why?

-Am I doing a 3-legged oAuth or an OOB oAuth?

-Why would I need the PIN then?

-How am I supposed to use the PIN correctly (if I need it)?

-How am I supposed to authenticate without the PIN (if I DON'T need it)?

-How do I make it so that users won't always see the PIN page after authenticating one time? I could put a callback in the very first request, but what if I don't want the user to get redirected to ANY page at all?

Am I doing a 3-legged oAuth or an OOB oAuth?

You are doing both. 3-legged means you are involving a user, 2-legged is business to business, or service to service. OOB (Out of band) means that you automatically trigger the PIN-based authentication scheme. Basically this means that you are saying that you cannot receive the normal oauth_verifier parameter without the user manually entering it as a PIN.

Why would I need the PIN then?

You get the PIN because you are stating your callback as OOB. If you set up a real callback you can instead receive the oauth_verifier directly to your application.

How am I supposed to use the PIN correctly (if I need it)?

You use it in the next step, when exchanging the request token for an access token you pass it along in the request as the oauth_verifier.

How am I supposed to authenticate without the PIN (if I DON'T need it)?

You need the PIN, or if you use a real callback, the oauth_verifier. They are the same thing, the only difference is that the PIN gets printed on the screen so a user can copy-paste it into your application, while the oauth_verifier is automatically picked up by your application.

How do I make it so that users won't always see the PIN page after authenticating one time? I could put a callback in the very first request, but what if I don't want the user to get redirected to ANY page at all?

You use a real callback that intercepts and uses the oauth_verifier.

-If I have logged in during the second code segment and have been directed to the PIN page, but then chose NOT to enter the PIN/enter some wrong PIN into my application, I still get successfully authenticated and can get the final tokens without any problems. Why?

This simply cannot be true. There must be a good reason for this, perhaps your app already has an access token and simply uses it?