[gigajew]

Just releasing this in case anyone wants to study or use it. It's a very easy-to-use wrapper for the PasteBin API. I created it for the user xCh3rx. It has the following methods:

PasteBin.Login(username, password);
PasteBin.Paste(paste contents, public/private, subject, syntax type);

You can get your developer key after creating an account at https://pastebin.com/api

Code

using System;
using System.Collections.Specialized;
using System.Net;
using System.IO;

namespace HackForums {
    
    public class Demo {
        
        public static void Main(string[] argv) {
            var username = ""; //username
            var password = ""; //password
            var developer = ""; //developer key
            
            using(var pastebin = new PasteBin(developer)) {
                if(pastebin.Login(username, password)) {
                    var link = pastebin.Paste("Hello world"); //return pastebin link
                    Console.WriteLine(link);
                }
            }
        }
    }
    
    //Created by GigaJew
    public class PasteBin : IDisposable {
        
        private WebClient Client { get; set; }
        
        public string BaseUrl {
            get {
                return "http://pastebin.com/api/";
            }
        }
        
        public string LoginUrl {
            get {
                return Path.Combine(this.BaseUrl, "api_login.php");
            }
        }
        
        public string PasteUrl {
            get {
                return Path.Combine(this.BaseUrl, "api_post.php");
            }
        }
        
        public bool LoggedIn {
            get {
                return !string.IsNullOrEmpty(this.UserKey);
            }
        }
        
        public string DevKey { get; set; }
        
        public string UserKey { get; set; }
        
        public PasteBin(string devkey) {
            this.Client = new WebClient() {
                Proxy = null
            };
            this.DevKey = devkey;
        }
        
        public PasteBin() {
            this.Client = new WebClient() {
                Proxy = null
            };
        }
        
        public string Paste(string body, bool @private = false, string subject = "", string format = "text") {
            if(!this.LoggedIn) {
                throw new Exception("Not logged in");
            }
            
            var response = this.Client.UploadValues(this.PasteUrl, new NameValueCollection() {
                { "api_dev_key", this.DevKey },
                { "api_option", "paste" },
                { "api_paste_code", body },
                { "api_paste_private", @private ? "0" : "1" },
                { "api_paste_name", subject },
                { "api_paste_expire_date", "N" },
                { "api_paste_format", format },
                { "api_user_key", this.UserKey }
            });
            
            using (MemoryStream memory = new MemoryStream(response)) {
                using (StreamReader reader = new StreamReader(memory)) {
                    var link = reader.ReadLine();
                    if(link.IndexOf("Bad") == -1) {
                        return link;
                    }else {
                        throw new Exception(link);
                    }
                }
            }
            
        }
        
        public bool Login(string username, string password) {
            if(string.IsNullOrEmpty(this.DevKey)) {
                throw new Exception("No developer key specified");
            }
            
            var response = this.Client.UploadValues(this.LoginUrl, new NameValueCollection() {
                { "api_dev_key", this.DevKey },
                { "api_user_name", username },
                { "api_user_password", password }
            });
            
            using (MemoryStream memory = new MemoryStream(response)) {
                using (StreamReader reader = new StreamReader(memory)) {
                    var key = reader.ReadLine();
                    if(key.IndexOf("Bad") == -1) {
                        this.UserKey = key;
                        return true;
                    }else {
                        return false;
                    }
                }
            }
        }
        
        public void Dispose() {
            this.Client.Dispose();
        }
    }
    
}

[Visual Freedom]

Sime yet effective. This is a good way to start with a pastebin integration.

[Ninja]

Why a private property instead of a field? Just use a field. A property is used to 'protect' a field from outside sources.
Why are BaseURL, LoginURL, PasteURL. all public?
Why not set a bool for the LoggedIn property instead of a string nullcheck condition?