add some auth helpers

src/Untappd.Net/Authentication/AuthenticationHelper.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Untappd.Net.Client;
+using Untappd.Net.Request;
+
+namespace Untappd.Net.Authentication
+{
+    public static class AuthenticationHelper
+    {
+        /// <summary>
+        /// Redirect the user to this string.
+        /// </summary>
+        /// <param name="credentials"></param>
+        /// <param name="redirectUrl">The URL to redirect back to your application. Should listen on code as a string param</param>
+        /// <returns></returns>
+        public static string RedirectUserTo(IUnAuthenticadedUntappdCredentials credentials, string redirectUrl)
+        {
+            return string.Format("{0}/?client_id={1}&response_type=code&redirect_url={2}", Constants.BaseRequestString,
+                credentials.ClientId, redirectUrl);
+        }
+
+        /// <summary>
+        /// Url to get the OAuth token.
+        /// </summary>
+        /// <param name="credentials"></param>
+        /// <param name="redirectUrl"></param>
+        /// <param name="code">Data returned by the initial request(see: RedirectUserTo)</param>
+        /// <returns></returns>
+        public static string TokenUrl(IUnAuthenticadedUntappdCredentials credentials, string redirectUrl, string code)
+        {
+            return string.Format("{0}/?client_id={1}&client_secret={2}&response_type=code&redirect_url={3}&code={4}", 
+                Constants.OAuthTokenEndPoint, 
+                credentials.ClientId, 
+                credentials.ClientSecret,
+                redirectUrl, 
+                code);
+        }
+    }
+}

src/Untappd.Net/Constants.cs

@@ -3,5 +3,6 @@
     public struct Constants
     {
         public const string BaseRequestString = "https://api.untappd.com";
+        public const string OAuthTokenEndPoint = "https://untappd.com/oauth/authorize";
     }
 }

src/Untappd.Net/Untappd.Net.csproj

@@ -46,6 +46,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Authentication\AuthenticationHelper.cs" />
     <Compile Include="Client\AuthenticatedUntappdCredentials.cs" />
     <Compile Include="Client\IAuthenticatedUntappdCredentials.cs" />
     <Compile Include="Client\IUnAuthenticadedUntappdCredentials.cs" />