Support ValidateTwoFactorPIN with iterationOffset as parameter

Google.Authenticator.Tests/ValidationTests.cs

@@ -28,6 +28,9 @@ public void ValidateWorksWithDifferentSecretTypes(string pin, int irrelevantNumb
             subject.ValidateTwoFactorPIN(secretAsBytes, pin, TimeSpan.FromMinutes(irrelevantNumberToAvoidDuplicatePinsBeingRemoved));
             subject.ValidateTwoFactorPIN(secretAsBase32, pin, true);
             subject.ValidateTwoFactorPIN(secretAsBase32, pin, TimeSpan.FromMinutes(irrelevantNumberToAvoidDuplicatePinsBeingRemoved), true);
+            subject.ValidateTwoFactorPIN(secret, pin, irrelevantNumberToAvoidDuplicatePinsBeingRemoved * 2, false);
+            subject.ValidateTwoFactorPIN(secretAsBase32, pin, irrelevantNumberToAvoidDuplicatePinsBeingRemoved * 2, true);
+            subject.ValidateTwoFactorPIN(secretAsBytes, pin, irrelevantNumberToAvoidDuplicatePinsBeingRemoved * 2);
         }
 
         public static IEnumerable<object[]> GetPins()

Google.Authenticator/TwoFactorAuthenticator.cs

@@ -202,11 +202,30 @@ public bool ValidateTwoFactorPIN(byte[] accountSecretKey, string twoFactorCodeFr
         /// <param name="twoFactorCodeFromClient">The PIN from the client</param>
         /// <param name="timeTolerance">The time window within which to check to allow for clock drift between devices.</param>
         /// <returns>True if PIN is currently valid</returns>
-        public bool ValidateTwoFactorPIN(byte[] accountSecretKey, string twoFactorCodeFromClient, TimeSpan timeTolerance)
-        {
-            return GetCurrentPINs(accountSecretKey, timeTolerance).Any(c => c == twoFactorCodeFromClient);
-        }
+        public bool ValidateTwoFactorPIN(byte[] accountSecretKey, string twoFactorCodeFromClient, TimeSpan timeTolerance) => 
+            GetCurrentPINs(accountSecretKey, timeTolerance).Any(c => c == twoFactorCodeFromClient);
 
+        /// <summary>
+        /// Given a PIN from a client, check if it is valid at the current time.
+        /// </summary>
+        /// <param name="accountSecretKey">Account Secret Key</param>
+        /// <param name="twoFactorCodeFromClient">The PIN from the client</param>
+        /// <param name="iterationOffset">The counter window within which to check to allow for clock drift between devices.</param>
+        /// <param name="secretIsBase32">Flag saying if accountSecretKey is in Base32 format or original secret</param>
+        /// <returns>True if PIN is currently valid</returns>
+        public bool ValidateTwoFactorPIN(string accountSecretKey, string twoFactorCodeFromClient, int iterationOffset, bool secretIsBase32 = false) => 
+            ValidateTwoFactorPIN(ConvertSecretToBytes(accountSecretKey, secretIsBase32), twoFactorCodeFromClient, iterationOffset);
+
+        /// <summary>
+        /// Given a PIN from a client, check if it is valid at the current time.
+        /// </summary>
+        /// <param name="accountSecretKey">Account Secret Key</param>
+        /// <param name="twoFactorCodeFromClient">The PIN from the client</param>
+        /// <param name="iterationOffset">The counter window within which to check to allow for clock drift between devices.</param>
+        /// <returns>True if PIN is currently valid</returns>
+        public bool ValidateTwoFactorPIN(byte[] accountSecretKey, string twoFactorCodeFromClient, int iterationOffset) => 
+            GetCurrentPINs(accountSecretKey, iterationOffset).Any(c => c == twoFactorCodeFromClient);
+
         /// <summary>
         /// Get the PIN for current time; the same code that a 2FA app would generate for the current time.
         /// Do not validate directly against this as clockdrift may cause a a different PIN to be generated than one you did a second ago.
@@ -282,15 +301,25 @@ public string[] GetCurrentPINs(byte[] accountSecretKey) =>
         /// <returns></returns>
         public string[] GetCurrentPINs(byte[] accountSecretKey, TimeSpan timeTolerance)
         {
-            var codes = new List<string>();
-            var iterationCounter = GetCurrentCounter();
             var iterationOffset = 0;
 
             if (timeTolerance.TotalSeconds > 30)
-            {
                 iterationOffset = Convert.ToInt32(timeTolerance.TotalSeconds / 30.00);
-            }
 
+            return GetCurrentPINs(accountSecretKey, iterationOffset);
+        }
+
+        /// <summary>
+        /// Get all the PINs that would be valid within the time window allowed for by the specified clock drift.
+        /// </summary>
+        /// <param name="accountSecretKey">Account Secret Key</param>
+        /// <param name="iterationOffset">The counter drift size you want to generate PINs for</param>
+        /// <returns></returns>
+        public string[] GetCurrentPINs(byte[] accountSecretKey, int iterationOffset)
+        {
+            var codes = new List<string>();
+            var iterationCounter = GetCurrentCounter();
+
             var iterationStart = iterationCounter - iterationOffset;
             var iterationEnd = iterationCounter + iterationOffset;