Merge branch 'retargeting-contracts'

29 files changed, 61 insertions, 290 deletions

diff --git a/src/DotNetOpenAuth.OpenId.Provider/DotNetOpenAuth.OpenId.Provider.csproj b/src/DotNetOpenAuth.OpenId.Provider/DotNetOpenAuth.OpenId.Provider.csproj
index 524415f..d9fd749 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/DotNetOpenAuth.OpenId.Provider.csproj
+++ b/src/DotNetOpenAuth.OpenId.Provider/DotNetOpenAuth.OpenId.Provider.csproj
@@ -35,7 +35,6 @@
     <Compile Include="OpenId\Messages\IAssociateRequestProvider.cs" />
     <Compile Include="OpenId\Messages\AssociateRequestProviderTools.cs" />
     <Compile Include="OpenId\Messages\IAssociateSuccessfulResponseProvider.cs" />
-    <Compile Include="OpenId\Messages\IAssociateSuccessfulResponseProviderContract.cs" />
     <Compile Include="OpenId\Messages\AssociateUnencryptedResponseProvider.cs" />
     <Compile Include="OpenId\Messages\CheckAuthenticationResponseProvider.cs" />
     <Compile Include="OpenId\Provider\OpenIdProviderUtilities.cs" />
@@ -53,7 +52,6 @@
     <Compile Include="OpenId\Provider\IDirectedIdentityIdentifierProvider.cs" />
     <Compile Include="OpenId\Provider\IErrorReporting.cs" />
     <Compile Include="OpenId\Provider\Request.cs" />
-    <Compile Include="OpenId\Provider\RequestContract.cs" />
     <Compile Include="OpenId\Provider\StandardProviderApplicationStore.cs" />
     <Compile Include="OpenId\Provider\OpenIdProvider.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
@@ -67,17 +65,24 @@
       <Project>{3896A32A-E876-4C23-B9B8-78E17D134CD3}</Project>
       <Name>DotNetOpenAuth.OpenId</Name>
     </ProjectReference>
-    <ProjectReference Include="..\Org.Mentalis.Security.Cryptography\Org.Mentalis.Security.Cryptography.csproj" >
+    <ProjectReference Include="..\Org.Mentalis.Security.Cryptography\Org.Mentalis.Security.Cryptography.csproj">
       <Project>{26DC877F-5987-48DD-9DDB-E62F2DE0E150}</Project>
       <Name>Org.Mentalis.Security.Cryptography</Name>
     </ProjectReference>
   </ItemGroup>
   <ItemGroup>
     <Reference Include="System" />
+    <Reference Include="Validation, Version=2.0.0.0, Culture=neutral, PublicKeyToken=2fc06f0d701809a7, processorArchitecture=MSIL">
+      <SpecificVersion>False</SpecificVersion>
+      <HintPath>..\packages\Validation.2.0.0.12319\lib\portable-windows8+net40+sl5+windowsphone8\Validation.dll</HintPath>
+    </Reference>
   </ItemGroup>
   <ItemGroup>
     <Folder Include="Configuration\" />
   </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Import Project="$(ProjectRoot)tools\DotNetOpenAuth.targets" />
   <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildProjectDirectory), EnlistmentInfo.targets))\EnlistmentInfo.targets" Condition=" '$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildProjectDirectory), EnlistmentInfo.targets))' != '' " />
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/OpenIdProviderChannel.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/OpenIdProviderChannel.cs
index c18bcac..45a69a5 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/OpenIdProviderChannel.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/OpenIdProviderChannel.cs
@@ -7,13 +7,13 @@
 namespace DotNetOpenAuth.OpenId.ChannelElements {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.Messaging.Bindings;
 	using DotNetOpenAuth.OpenId.Extensions;
 	using DotNetOpenAuth.OpenId.Provider;
+	using Validation;
 
 	/// <summary>
 	/// The messaging channel for OpenID Providers.
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/ProviderSigningBindingElement.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/ProviderSigningBindingElement.cs
index 93d86d2..fbbf37a 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/ProviderSigningBindingElement.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/ChannelElements/ProviderSigningBindingElement.cs
@@ -7,7 +7,6 @@
 namespace DotNetOpenAuth.OpenId.ChannelElements {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using System.Web;
@@ -16,6 +15,7 @@ namespace DotNetOpenAuth.OpenId.ChannelElements {
 	using DotNetOpenAuth.Messaging.Reflection;
 	using DotNetOpenAuth.OpenId.Messages;
 	using DotNetOpenAuth.OpenId.Provider;
+	using Validation;
 
 	/// <summary>
 	/// The signing binding element for OpenID Providers.
@@ -217,7 +217,7 @@ namespace DotNetOpenAuth.OpenId.ChannelElements {
 		/// the inclusion and order of message parts that will be signed.
 		/// </returns>
 		private string GetSignedParameterOrder(ITamperResistantOpenIdMessage signedMessage) {
-			Requires.ValidState(this.Channel != null);
+			RequiresEx.ValidState(this.Channel != null);
 			Requires.NotNull(signedMessage, "signedMessage");
 
 			Protocol protocol = Protocol.Lookup(signedMessage.Version);
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateDiffieHellmanProviderResponse.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateDiffieHellmanProviderResponse.cs
index c7e0ad9..ebcb534 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateDiffieHellmanProviderResponse.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateDiffieHellmanProviderResponse.cs
@@ -6,7 +6,6 @@
 
 namespace DotNetOpenAuth.OpenId.Messages {
 	using System;
-	using System.Diagnostics.Contracts;
 	using System.Security.Cryptography;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.Messaging.Reflection;
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateRequestProviderTools.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateRequestProviderTools.cs
index 0fb5e98..a03c93f 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateRequestProviderTools.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/AssociateRequestProviderTools.cs
@@ -7,11 +7,11 @@
 namespace DotNetOpenAuth.OpenId.Messages {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Provider;
+	using Validation;
 
 	/// <summary>
 	/// OpenID Provider tools for receiving association requests.
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/CheckAuthenticationResponseProvider.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/CheckAuthenticationResponseProvider.cs
index c187d5e..f69de5e 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/CheckAuthenticationResponseProvider.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/CheckAuthenticationResponseProvider.cs
@@ -7,11 +7,11 @@
 namespace DotNetOpenAuth.OpenId.Messages {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.OpenId.ChannelElements;
 	using DotNetOpenAuth.OpenId.Provider;
+	using Validation;
 
 	/// <summary>
 	/// The check_auth response message, as it is seen by the OpenID Provider.
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/IAssociateSuccessfulResponseProvider.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/IAssociateSuccessfulResponseProvider.cs
index 070f235..df02a2c 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/IAssociateSuccessfulResponseProvider.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/IAssociateSuccessfulResponseProvider.cs
@@ -7,7 +7,6 @@
 namespace DotNetOpenAuth.OpenId.Messages {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
@@ -16,7 +15,6 @@ namespace DotNetOpenAuth.OpenId.Messages {
 	/// <summary>
 	/// An outgoing successful association response from the OpenID Provider.
 	/// </summary>
-	[ContractClass(typeof(IAssociateSuccessfulResponseProviderContract))]
 	internal interface IAssociateSuccessfulResponseProvider : IProtocolMessage {
 		/// <summary>
 		/// Gets or sets the expires in.
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/IAssociateSuccessfulResponseProviderContract.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/IAssociateSuccessfulResponseProviderContract.cs
deleted file mode 100644
index 6788a84..0000000
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Messages/IAssociateSuccessfulResponseProviderContract.cs
+++ /dev/null
@@ -1,96 +0,0 @@
-//-----------------------------------------------------------------------
-// <copyright file="IAssociateSuccessfulResponseProviderContract.cs" company="Outercurve Foundation">
-//     Copyright (c) Outercurve Foundation. All rights reserved.
-// </copyright>
-//-----------------------------------------------------------------------
-
-namespace DotNetOpenAuth.OpenId.Messages {
-	using System;
-	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
-	using System.Linq;
-	using System.Text;
-	using DotNetOpenAuth.Messaging;
-	using DotNetOpenAuth.OpenId.Provider;
-
-	/// <summary>
-	/// Code contract for the <see cref="IAssociateSuccessfulResponseProvider"/> interface.
-	/// </summary>
-	[ContractClassFor(typeof(IAssociateSuccessfulResponseProvider))]
-	internal abstract class IAssociateSuccessfulResponseProviderContract : IAssociateSuccessfulResponseProvider {
-		/// <summary>
-		/// Gets or sets the expires in.
-		/// </summary>
-		/// <value>
-		/// The expires in.
-		/// </value>
-		long IAssociateSuccessfulResponseProvider.ExpiresIn {
-			get { throw new NotImplementedException();  }
-			set { throw new NotImplementedException(); }
-		}
-
-		/// <summary>
-		/// Gets or sets the association handle.
-		/// </summary>
-		/// <value>
-		/// The association handle.
-		/// </value>
-		string IAssociateSuccessfulResponseProvider.AssociationHandle {
-			get { throw new NotImplementedException(); }
-			set { throw new NotImplementedException(); }
-		}
-
-		/// <summary>
-		/// Gets the level of protection this message requires.
-		/// </summary>
-		Messaging.MessageProtections Messaging.IProtocolMessage.RequiredProtection {
-			get { throw new NotImplementedException(); }
-		}
-
-		/// <summary>
-		/// Gets a value indicating whether this is a direct or indirect message.
-		/// </summary>
-		Messaging.MessageTransport Messaging.IProtocolMessage.Transport {
-			get { throw new NotImplementedException(); }
-		}
-
-		/// <summary>
-		/// Gets the version of the protocol or extension this message is prepared to implement.
-		/// </summary>
-		Version Messaging.IMessage.Version {
-			get { throw new NotImplementedException(); }
-		}
-
-		/// <summary>
-		/// Gets the extra, non-standard Protocol parameters included in the message.
-		/// </summary>
-		IDictionary<string, string> Messaging.IMessage.ExtraData {
-			get { throw new NotImplementedException(); }
-		}
-
-		/// <summary>
-		/// Called to create the Association based on a request previously given by the Relying Party.
-		/// </summary>
-		/// <param name="request">The prior request for an association.</param>
-		/// <param name="associationStore">The Provider's association store.</param>
-		/// <param name="securitySettings">The security settings of the Provider.</param>
-		/// <returns>
-		/// The created association.
-		/// </returns>
-		Association IAssociateSuccessfulResponseProvider.CreateAssociationAtProvider(AssociateRequest request, IProviderAssociationStore associationStore, ProviderSecuritySettings securitySettings) {
-			Requires.NotNull(request, "request");
-			Requires.NotNull(associationStore, "associationStore");
-			Requires.NotNull(securitySettings, "securitySettings");
-			throw new NotImplementedException();
-		}
-
-		/// <summary>
-		/// Checks the message state for conformity to the protocol specification
-		/// and throws an exception if the message is invalid.
-		/// </summary>
-		/// <exception cref="ProtocolException">Thrown if the message is invalid.</exception>
-		void Messaging.IMessage.EnsureValidMessage() {
-			throw new NotImplementedException();
-		}
-	}
-}
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AnonymousRequest.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AnonymousRequest.cs
index f156b9a..9d73d9a 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AnonymousRequest.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AnonymousRequest.cs
@@ -7,9 +7,9 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Messages;
+	using Validation;
 
 	/// <summary>
 	/// Provides access to a host Provider to read an incoming extension-only checkid request message,
@@ -31,7 +31,7 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		internal AnonymousRequest(OpenIdProvider provider, SignedResponseRequest request)
 			: base(provider, request) {
 			Requires.NotNull(provider, "provider");
-			Requires.True(!(request is CheckIdRequest), "request");
+			Requires.That(!(request is CheckIdRequest), "request", "request cannot be CheckIdRequest");
 
 			this.positiveResponse = new IndirectSignedResponse(request);
 		}
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AssociationDataBag.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AssociationDataBag.cs
index f619b76..350ed5f 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AssociationDataBag.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AssociationDataBag.cs
@@ -7,12 +7,12 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.IO;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.Messaging.Bindings;
+	using Validation;
 
 	/// <summary>
 	/// A signed and encrypted serialization of an association.
@@ -58,6 +58,9 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// </summary>
 		/// <param name="stream">The stream.</param>
 		public void Serialize(Stream stream) {
+			Requires.NotNull(stream, "stream");
+			Requires.That(stream.CanWrite, "stream", "requires stream.CanWrite");
+
 			var writer = new BinaryWriter(stream);
 			writer.Write(this.IsPrivateAssociation);
 			writer.WriteBuffer(this.Secret);
@@ -70,6 +73,9 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// </summary>
 		/// <param name="stream">The stream.</param>
 		public void Deserialize(Stream stream) {
+			Requires.NotNull(stream, "stream");
+			Requires.That(stream.CanRead, "stream", "requires stream.CanRead");
+
 			var reader = new BinaryReader(stream);
 			this.IsPrivateAssociation = reader.ReadBoolean();
 			this.Secret = reader.ReadBuffer(256);
@@ -88,7 +94,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		internal static IDataBagFormatter<AssociationDataBag> CreateFormatter(ICryptoKeyStore cryptoKeyStore, string bucket, TimeSpan? minimumAge = null) {
 			Requires.NotNull(cryptoKeyStore, "cryptoKeyStore");
 			Requires.NotNullOrEmpty(bucket, "bucket");
-			Contract.Ensures(Contract.Result<IDataBagFormatter<AssociationDataBag>>() != null);
 			return new BinaryDataBagFormatter<AssociationDataBag>(cryptoKeyStore, bucket, signed: true, encrypted: true, minimumAge: minimumAge);
 		}
 	}
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AuthenticationRequest.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AuthenticationRequest.cs
index e88af8a..0167580 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AuthenticationRequest.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AuthenticationRequest.cs
@@ -6,9 +6,9 @@
 
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
-	using System.Diagnostics.Contracts;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Messages;
+	using Validation;
 
 	/// <summary>
 	/// Implements the <see cref="IAuthenticationRequest"/> interface
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AutoResponsiveRequest.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AutoResponsiveRequest.cs
index 661d719..91bb6f3 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AutoResponsiveRequest.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/AutoResponsiveRequest.cs
@@ -7,11 +7,11 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Messages;
+	using Validation;
 
 	/// <summary>
 	/// Handles messages coming into an OpenID Provider for which the entire
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/GsaIcamProfile.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/GsaIcamProfile.cs
index feb56eb..e12ca39 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/GsaIcamProfile.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/GsaIcamProfile.cs
@@ -7,7 +7,6 @@
 namespace DotNetOpenAuth.OpenId.Provider.Behaviors {
 	using System;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using DotNetOpenAuth.Configuration;
 	using DotNetOpenAuth.Messaging;
@@ -17,6 +16,7 @@ namespace DotNetOpenAuth.OpenId.Provider.Behaviors {
 	using DotNetOpenAuth.OpenId.Extensions.SimpleRegistration;
 	using DotNetOpenAuth.OpenId.Provider;
 	using DotNetOpenAuth.OpenId.RelyingParty;
+	using Validation;
 
 	/// <summary>
 	/// Implements the Identity, Credential, &amp; Access Management (ICAM) OpenID 2.0 Profile
@@ -182,8 +182,8 @@ namespace DotNetOpenAuth.OpenId.Provider.Behaviors {
 		/// <param name="maximumLifetime">The maximum lifetime.</param>
 		/// <param name="securitySettings">The security settings to adjust.</param>
 		private static void SetMaximumAssociationLifetimeToNotExceed(string associationType, TimeSpan maximumLifetime, ProviderSecuritySettings securitySettings) {
-			Contract.Requires(!string.IsNullOrEmpty(associationType));
-			Contract.Requires(maximumLifetime.TotalSeconds > 0);
+			Requires.NotNullOrEmpty(associationType, "associationType");
+			Requires.That(maximumLifetime.TotalSeconds > 0, "maximumLifetime", "requires positive timespan");
 			if (!securitySettings.AssociationLifetimes.ContainsKey(associationType) ||
 				securitySettings.AssociationLifetimes[associationType] > maximumLifetime) {
 				securitySettings.AssociationLifetimes[associationType] = maximumLifetime;
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/PpidGeneration.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/PpidGeneration.cs
index 9b914d0..c8bdd93 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/PpidGeneration.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Behaviors/PpidGeneration.cs
@@ -7,7 +7,6 @@
 namespace DotNetOpenAuth.OpenId.Provider.Behaviors {
 	using System;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Behaviors;
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/ExtensionsInteropHelper.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/ExtensionsInteropHelper.cs
index 946d354..d4332d2 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/ExtensionsInteropHelper.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/ExtensionsInteropHelper.cs
@@ -8,13 +8,13 @@ namespace DotNetOpenAuth.OpenId.Provider.Extensions {
 	using System;
 	using System.Collections.Generic;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Extensions;
 	using DotNetOpenAuth.OpenId.Extensions.AttributeExchange;
 	using DotNetOpenAuth.OpenId.Extensions.SimpleRegistration;
 	using DotNetOpenAuth.OpenId.Messages;
+	using Validation;
 
 	/// <summary>
 	/// A set of methods designed to assist in improving interop across different
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/UI/UIRequestTools.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/UI/UIRequestTools.cs
index c5ede8c..278ad6c 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/UI/UIRequestTools.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Extensions/UI/UIRequestTools.cs
@@ -8,7 +8,6 @@ namespace DotNetOpenAuth.OpenId.Provider.Extensions.UI {
 	using System;
 	using System.Collections.Generic;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using System.Globalization;
 	using System.Linq;
 	using DotNetOpenAuth.Messaging;
@@ -16,6 +15,7 @@ namespace DotNetOpenAuth.OpenId.Provider.Extensions.UI {
 	using DotNetOpenAuth.OpenId.Messages;
 	using DotNetOpenAuth.OpenId.Provider;
 	using DotNetOpenAuth.Xrds;
+	using Validation;
 
 	/// <summary>
 	/// OpenID User Interface extension 1.0 request message.
@@ -52,8 +52,8 @@ namespace DotNetOpenAuth.OpenId.Provider.Extensions.UI {
 		/// </example>
 		/// </remarks>
 		public static IEnumerable<Uri> GetRelyingPartyIconUrls(Realm realm, IDirectWebRequestHandler webRequestHandler) {
-			Contract.Requires(realm != null);
-			Contract.Requires(webRequestHandler != null);
+			Requires.NotNull(realm, "realm");
+			Requires.NotNull(webRequestHandler, "webRequestHandler");
 			ErrorUtilities.VerifyArgumentNotNull(realm, "realm");
 			ErrorUtilities.VerifyArgumentNotNull(webRequestHandler, "webRequestHandler");
 
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HmacShaAssociationProvider.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HmacShaAssociationProvider.cs
index bdf3e9b..8c4011b 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HmacShaAssociationProvider.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HmacShaAssociationProvider.cs
@@ -7,11 +7,11 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Provider;
+	using Validation;
 
 	/// <summary>
 	/// OpenID Provider utility methods for HMAC-SHA* associations.
@@ -43,7 +43,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 			Requires.NotNullOrEmpty(associationType, "associationType");
 			Requires.NotNull(associationStore, "associationStore");
 			Requires.NotNull(securitySettings, "securitySettings");
-			Contract.Ensures(Contract.Result<HmacShaAssociation>() != null);
 
 			int secretLength = HmacShaAssociation.GetSecretLength(protocol, associationType);
 
@@ -61,9 +60,9 @@ namespace DotNetOpenAuth.OpenId.Provider {
 
 			string handle = associationStore.Serialize(secret, DateTime.UtcNow + lifetime, associationUse == AssociationRelyingPartyType.Dumb);
 
-			Contract.Assert(protocol != null); // All the way up to the method call, the condition holds, yet we get a Requires failure next
-			Contract.Assert(secret != null);
-			Contract.Assert(!string.IsNullOrEmpty(associationType));
+			Assumes.True(protocol != null); // All the way up to the method call, the condition holds, yet we get a Requires failure next
+			Assumes.True(secret != null);
+			Assumes.True(!string.IsNullOrEmpty(associationType));
 			var result = HmacShaAssociation.Create(protocol, associationType, handle, secret, lifetime);
 			return result;
 		}
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HostProcessedRequest.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HostProcessedRequest.cs
index 67ecdb2..9c5004c 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HostProcessedRequest.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/HostProcessedRequest.cs
@@ -7,12 +7,12 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Net;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Messages;
+	using Validation;
 
 	/// <summary>
 	/// A base class from which identity and non-identity RP requests can derive.
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IDirectedIdentityIdentifierProvider.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IDirectedIdentityIdentifierProvider.cs
index 86c7e7c..550033b 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IDirectedIdentityIdentifierProvider.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IDirectedIdentityIdentifierProvider.cs
@@ -7,6 +7,7 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Diagnostics.Contracts;
+	using Validation;
 
 	/// <summary>
 	/// An interface to provide custom identifiers for users logging into specific relying parties.
@@ -16,7 +17,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 	/// allowing the users to log into RPs without leaving any clue as to their true identity,
 	/// and preventing multiple RPs from colluding to track user activity across realms.
 	/// </remarks>
-	[ContractClass(typeof(IDirectedIdentityIdentifierProviderContract))]
 	public interface IDirectedIdentityIdentifierProvider {
 		/// <summary>
 		/// Gets the Identifier to use for the Claimed Identifier and Local Identifier of
@@ -40,44 +40,4 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		[Pure]
 		bool IsUserLocalIdentifier(Identifier identifier);
 	}
-
-	/// <summary>
-	/// Contract class for the <see cref="IDirectedIdentityIdentifierProvider"/> type.
-	/// </summary>
-	[ContractClassFor(typeof(IDirectedIdentityIdentifierProvider))]
-	internal abstract class IDirectedIdentityIdentifierProviderContract : IDirectedIdentityIdentifierProvider {
-		#region IDirectedIdentityIdentifierProvider Members
-
-		/// <summary>
-		/// Gets the Identifier to use for the Claimed Identifier and Local Identifier of
-		/// an outgoing positive assertion.
-		/// </summary>
-		/// <param name="localIdentifier">The OP local identifier for the authenticating user.</param>
-		/// <param name="relyingPartyRealm">The realm of the relying party receiving the assertion.</param>
-		/// <returns>
-		/// A valid, discoverable OpenID Identifier that should be used as the value for the
-		/// openid.claimed_id and openid.local_id parameters.  Must not be null.
-		/// </returns>
-		Uri IDirectedIdentityIdentifierProvider.GetIdentifier(Identifier localIdentifier, Realm relyingPartyRealm) {
-			Requires.NotNull(localIdentifier, "localIdentifier");
-			Requires.NotNull(relyingPartyRealm, "relyingPartyRealm");
-			Requires.True(((IDirectedIdentityIdentifierProvider)this).IsUserLocalIdentifier(localIdentifier), "localIdentifier", OpenIdStrings.ArgumentIsPpidIdentifier);
-			throw new NotImplementedException();
-		}
-
-		/// <summary>
-		/// Determines whether a given identifier is the primary (non-PPID) local identifier for some user.
-		/// </summary>
-		/// <param name="identifier">The identifier in question.</param>
-		/// <returns>
-		/// 	<c>true</c> if the given identifier is the valid, unique identifier for some uesr (and NOT a PPID); otherwise, <c>false</c>.
-		/// </returns>
-		bool IDirectedIdentityIdentifierProvider.IsUserLocalIdentifier(Identifier identifier) {
-			Requires.NotNull(identifier, "identifier");
-
-			throw new NotImplementedException();
-		}
-
-		#endregion
-	}
 }
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IProviderAssociationStore.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IProviderAssociationStore.cs
index 930abcd..e0f84b9 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IProviderAssociationStore.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/IProviderAssociationStore.cs
@@ -7,10 +7,10 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
+	using Validation;
 
 	/// <summary>
 	/// Provides association serialization and deserialization.
@@ -24,7 +24,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 	/// to avoid disclosing the secret to anyone who sees the association handle, which itself isn't considered to
 	/// be confidential.
 	/// </remarks>
-	[ContractClass(typeof(IProviderAssociationStoreContract))]
 	internal interface IProviderAssociationStore {
 		/// <summary>
 		/// Stores an association and returns a handle for it.
@@ -49,42 +48,4 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// <exception cref="ProtocolException">Thrown if the association is not of the expected type.</exception>
 		Association Deserialize(IProtocolMessage containingMessage, bool privateAssociation, string handle);
 	}
-
-	/// <summary>
-	/// Code contract for the <see cref="IProviderAssociationStore"/> interface.
-	/// </summary>
-	[ContractClassFor(typeof(IProviderAssociationStore))]
-	internal abstract class IProviderAssociationStoreContract : IProviderAssociationStore {
-		/// <summary>
-		/// Stores an association and returns a handle for it.
-		/// </summary>
-		/// <param name="secret">The association secret.</param>
-		/// <param name="expiresUtc">The expires UTC.</param>
-		/// <param name="privateAssociation">A value indicating whether this is a private association.</param>
-		/// <returns>
-		/// The association handle that represents this association.
-		/// </returns>
-		string IProviderAssociationStore.Serialize(byte[] secret, DateTime expiresUtc, bool privateAssociation) {
-			Requires.NotNull(secret, "secret");
-			Requires.True(expiresUtc.Kind == DateTimeKind.Utc, "expiresUtc");
-			Contract.Ensures(!string.IsNullOrEmpty(Contract.Result<string>()));
-			throw new NotImplementedException();
-		}
-
-		/// <summary>
-		/// Retrieves an association given an association handle.
-		/// </summary>
-		/// <param name="containingMessage">The OpenID message that referenced this association handle.</param>
-		/// <param name="privateAssociation">A value indicating whether a private association is expected.</param>
-		/// <param name="handle">The association handle.</param>
-		/// <returns>
-		/// An association instance, or <c>null</c> if the association has expired or the signature is incorrect (which may be because the OP's symmetric key has changed).
-		/// </returns>
-		/// <exception cref="ProtocolException">Thrown if the association is not of the expected type.</exception>
-		Association IProviderAssociationStore.Deserialize(IProtocolMessage containingMessage, bool privateAssociation, string handle) {
-			Requires.NotNull(containingMessage, "containingMessage");
-			Requires.NotNullOrEmpty(handle, "handle");
-			throw new NotImplementedException();
-		}
-	}
 }
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProvider.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProvider.cs
index 05a33bc..d96e5c9 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProvider.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProvider.cs
@@ -11,7 +11,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 	using System.Collections.Specialized;
 	using System.ComponentModel;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Threading;
 	using System.Web;
@@ -20,13 +19,13 @@ namespace DotNetOpenAuth.OpenId.Provider {
 	using DotNetOpenAuth.Messaging.Bindings;
 	using DotNetOpenAuth.OpenId.ChannelElements;
 	using DotNetOpenAuth.OpenId.Messages;
+	using Validation;
 	using RP = DotNetOpenAuth.OpenId.RelyingParty;
 
 	/// <summary>
 	/// Offers services for a web page that is acting as an OpenID identity server.
 	/// </summary>
 	[SuppressMessage("Microsoft.Maintainability", "CA1506:AvoidExcessiveClassCoupling", Justification = "By design")]
-	[ContractVerification(true)]
 	public sealed class OpenIdProvider : IDisposable, IOpenIdHost {
 		/// <summary>
 		/// The name of the key to use in the HttpApplication cache to store the
@@ -55,8 +54,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// </summary>
 		public OpenIdProvider()
 			: this(OpenIdElement.Configuration.Provider.ApplicationStore.CreateInstance(HttpApplicationStore)) {
-			Contract.Ensures(this.SecuritySettings != null);
-			Contract.Ensures(this.Channel != null);
 		}
 
 		/// <summary>
@@ -66,8 +63,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		public OpenIdProvider(IOpenIdApplicationStore applicationStore)
 			: this((INonceStore)applicationStore, (ICryptoKeyStore)applicationStore) {
 			Requires.NotNull(applicationStore, "applicationStore");
-			Contract.Ensures(this.SecuritySettings != null);
-			Contract.Ensures(this.Channel != null);
 		}
 
 		/// <summary>
@@ -78,8 +73,6 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		private OpenIdProvider(INonceStore nonceStore, ICryptoKeyStore cryptoKeyStore) {
 			Requires.NotNull(nonceStore, "nonceStore");
 			Requires.NotNull(cryptoKeyStore, "cryptoKeyStore");
-			Contract.Ensures(this.SecuritySettings != null);
-			Contract.Ensures(this.Channel != null);
 
 			this.SecuritySettings = OpenIdElement.Configuration.Provider.SecuritySettings.CreateSecuritySettings();
 			this.behaviors.CollectionChanged += this.OnBehaviorsChanged;
@@ -102,8 +95,7 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		[EditorBrowsable(EditorBrowsableState.Advanced)]
 		public static IOpenIdApplicationStore HttpApplicationStore {
 			get {
-				Requires.ValidState(HttpContext.Current != null && HttpContext.Current.Request != null, MessagingStrings.HttpContextRequired);
-				Contract.Ensures(Contract.Result<IOpenIdApplicationStore>() != null);
+				RequiresEx.ValidState(HttpContext.Current != null && HttpContext.Current.Request != null, MessagingStrings.HttpContextRequired);
 				HttpContext context = HttpContext.Current;
 				var store = (IOpenIdApplicationStore)context.Application[ApplicationStoreKey];
 				if (store == null) {
@@ -131,8 +123,7 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// </summary>
 		public ProviderSecuritySettings SecuritySettings {
 			get {
-				Contract.Ensures(Contract.Result<ProviderSecuritySettings>() != null);
-				Contract.Assume(this.securitySettings != null);
+				Assumes.True(this.securitySettings != null);
 				return this.securitySettings;
 			}
 
@@ -325,9 +316,9 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		[SuppressMessage("Microsoft.Performance", "CA1800:DoNotCastUnnecessarily", Justification = "Code Contract requires that we cast early.")]
 		[EditorBrowsable(EditorBrowsableState.Never)]
 		public void SendResponse(IRequest request) {
-			Requires.ValidState(HttpContext.Current != null, MessagingStrings.CurrentHttpContextRequired);
+			RequiresEx.ValidState(HttpContext.Current != null, MessagingStrings.CurrentHttpContextRequired);
 			Requires.NotNull(request, "request");
-			Requires.True(request.IsResponseReady, "request");
+			Requires.That(request.IsResponseReady, "request", OpenIdStrings.ResponseNotReady);
 
 			this.ApplyBehaviorsToResponse(request);
 			Request requestInternal = (Request)request;
@@ -346,9 +337,9 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// <exception cref="InvalidOperationException">Thrown if <see cref="IRequest.IsResponseReady"/> is <c>false</c>.</exception>
 		[SuppressMessage("Microsoft.Performance", "CA1800:DoNotCastUnnecessarily", Justification = "Code Contract requires that we cast early.")]
 		public void Respond(IRequest request) {
-			Requires.ValidState(HttpContext.Current != null, MessagingStrings.CurrentHttpContextRequired);
+			RequiresEx.ValidState(HttpContext.Current != null, MessagingStrings.CurrentHttpContextRequired);
 			Requires.NotNull(request, "request");
-			Requires.True(request.IsResponseReady, "request");
+			Requires.That(request.IsResponseReady, "request", OpenIdStrings.ResponseNotReady);
 
 			this.ApplyBehaviorsToResponse(request);
 			Request requestInternal = (Request)request;
@@ -364,7 +355,7 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		[SuppressMessage("Microsoft.Performance", "CA1800:DoNotCastUnnecessarily", Justification = "Code Contract requires that we cast early.")]
 		public OutgoingWebResponse PrepareResponse(IRequest request) {
 			Requires.NotNull(request, "request");
-			Requires.True(request.IsResponseReady, "request");
+			Requires.That(request.IsResponseReady, "request", OpenIdStrings.ResponseNotReady);
 
 			this.ApplyBehaviorsToResponse(request);
 			Request requestInternal = (Request)request;
@@ -387,9 +378,9 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// be the same as <paramref name="claimedIdentifier"/>.</param>
 		/// <param name="extensions">The extensions.</param>
 		public void SendUnsolicitedAssertion(Uri providerEndpoint, Realm relyingPartyRealm, Identifier claimedIdentifier, Identifier localIdentifier, params IExtensionMessage[] extensions) {
-			Requires.ValidState(HttpContext.Current != null, MessagingStrings.HttpContextRequired);
+			RequiresEx.ValidState(HttpContext.Current != null, MessagingStrings.HttpContextRequired);
 			Requires.NotNull(providerEndpoint, "providerEndpoint");
-			Requires.True(providerEndpoint.IsAbsoluteUri, "providerEndpoint");
+			Requires.That(providerEndpoint.IsAbsoluteUri, "providerEndpoint", OpenIdStrings.AbsoluteUriRequired);
 			Requires.NotNull(relyingPartyRealm, "relyingPartyRealm");
 			Requires.NotNull(claimedIdentifier, "claimedIdentifier");
 			Requires.NotNull(localIdentifier, "localIdentifier");
@@ -418,11 +409,11 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// </returns>
 		public OutgoingWebResponse PrepareUnsolicitedAssertion(Uri providerEndpoint, Realm relyingPartyRealm, Identifier claimedIdentifier, Identifier localIdentifier, params IExtensionMessage[] extensions) {
 			Requires.NotNull(providerEndpoint, "providerEndpoint");
-			Requires.True(providerEndpoint.IsAbsoluteUri, "providerEndpoint");
+			Requires.That(providerEndpoint.IsAbsoluteUri, "providerEndpoint", OpenIdStrings.AbsoluteUriRequired);
 			Requires.NotNull(relyingPartyRealm, "relyingPartyRealm");
 			Requires.NotNull(claimedIdentifier, "claimedIdentifier");
 			Requires.NotNull(localIdentifier, "localIdentifier");
-			Requires.ValidState(this.Channel.WebRequestHandler != null);
+			RequiresEx.ValidState(this.Channel.WebRequestHandler != null);
 
 			// Although the RP should do their due diligence to make sure that this OP
 			// is authorized to send an assertion for the given claimed identifier,
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProviderUtilities.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProviderUtilities.cs
index ae7dede..9e46168 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProviderUtilities.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/OpenIdProviderUtilities.cs
@@ -7,12 +7,12 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Messages;
 	using DotNetOpenAuth.OpenId.Provider;
+	using Validation;
 
 	/// <summary>
 	/// Utility methods for OpenID Providers.
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/PrivatePersonalIdentifierProviderBase.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/PrivatePersonalIdentifierProviderBase.cs
index aaffa4c..2650e44 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/PrivatePersonalIdentifierProviderBase.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/PrivatePersonalIdentifierProviderBase.cs
@@ -8,12 +8,12 @@ namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using System.Globalization;
 	using System.Linq;
 	using System.Security.Cryptography;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
+	using Validation;
 
 	/// <summary>
 	/// Provides standard PPID Identifiers to users to protect their identity from individual relying parties
@@ -102,7 +102,7 @@ namespace DotNetOpenAuth.OpenId.Provider {
 			}
 
 			set {
-				Requires.InRange(value > 0, "value");
+				Requires.Range(value > 0, "value");
 				this.newSaltLength = value;
 			}
 		}
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationHandleEncoder.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationHandleEncoder.cs
index 897b4f8..240e450 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationHandleEncoder.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationHandleEncoder.cs
@@ -6,11 +6,11 @@
 
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
-	using System.Diagnostics.Contracts;
 	using System.Threading;
 	using DotNetOpenAuth.Configuration;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.Messaging.Bindings;
+	using Validation;
 
 	/// <summary>
 	/// Provides association storage in the association handle itself, but embedding signed and encrypted association
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationKeyStorage.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationKeyStorage.cs
index 0786828..8eaae09 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationKeyStorage.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/ProviderAssociationKeyStorage.cs
@@ -6,9 +6,9 @@
 
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
-	using System.Diagnostics.Contracts;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.Messaging.Bindings;
+	using Validation;
 
 	/// <summary>
 	/// An association storage mechanism that stores the association secrets in a private store,
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Request.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Request.cs
index 21c1b51..ceabab3 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Request.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/Request.cs
@@ -7,19 +7,17 @@
 namespace DotNetOpenAuth.OpenId.Provider {
 	using System;
 	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OpenId.Messages;
+	using Validation;
 
 	/// <summary>
 	/// Implements the <see cref="IRequest"/> interface for all incoming
 	/// request messages to an OpenID Provider.
 	/// </summary>
 	[Serializable]
-	[ContractClass(typeof(RequestContract))]
-	[ContractVerification(true)]
 	internal abstract class Request : IRequest {
 		/// <summary>
 		/// The incoming request message.
@@ -99,8 +97,7 @@ namespace DotNetOpenAuth.OpenId.Provider {
 		/// <exception cref="InvalidOperationException">Thrown if <see cref="IsResponseReady"/> is <c>false</c>.</exception>
 		internal IProtocolMessage Response {
 			get {
-				Requires.ValidState(this.IsResponseReady, OpenIdStrings.ResponseNotReady);
-				Contract.Ensures(Contract.Result<IProtocolMessage>() != null);
+				RequiresEx.ValidState(this.IsResponseReady, OpenIdStrings.ResponseNotReady);
 
 				if (this.responseExtensions.Count > 0) {
 					var extensibleResponse = this.ResponseMessage as IProtocolMessageWithExtensions;
diff --git a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/RequestContract.cs b/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/RequestContract.cs
deleted file mode 100644
index aa692d3..0000000
--- a/src/DotNetOpenAuth.OpenId.Provider/OpenId/Provider/RequestContract.cs
+++ /dev/null
@@ -1,48 +0,0 @@
-//-----------------------------------------------------------------------
-// <copyright file="RequestContract.cs" company="Outercurve Foundation">
-//     Copyright (c) Outercurve Foundation. All rights reserved.
-// </copyright>
-//-----------------------------------------------------------------------
-
-namespace DotNetOpenAuth.OpenId.Provider {
-	using System;
-	using System.Collections.Generic;
-	using System.Diagnostics.Contracts;
-	using System.Linq;
-	using System.Text;
-	using DotNetOpenAuth.Messaging;
-
-	/// <summary>
-	/// Code contract for the <see cref="Request"/> class.
-	/// </summary>
-	[ContractClassFor(typeof(Request))]
-	internal abstract class RequestContract : Request {
-		/// <summary>
-		/// Prevents a default instance of the <see cref="RequestContract"/> class from being created.
-		/// </summary>
-		private RequestContract() : base((Version)null, null) {
-		}
-
-		/// <summary>
-		/// Gets a value indicating whether the response is ready to be sent to the user agent.
-		/// </summary>
-		/// <remarks>
-		/// This property returns false if there are properties that must be set on this
-		/// request instance before the response can be sent.
-		/// </remarks>
-		public override bool IsResponseReady {
-			get { throw new NotImplementedException(); }
-		}
-
-		/// <summary>
-		/// Gets the response message, once <see cref="IsResponseReady"/> is <c>true</c>.
-		/// </summary>
-		protected override IProtocolMessage ResponseMessage {
-			get {
-				Requires.ValidState(this.IsResponseReady);
-				Contract.Ensures(Contract.Result<IProtocolMessage>() != null);
-				throw new NotImplementedException();
-			}
-		}
-	}
-}
diff --git a/src/DotNetOpenAuth.OpenId.Provider/Properties/AssemblyInfo.cs b/src/DotNetOpenAuth.OpenId.Provider/Properties/AssemblyInfo.cs
index 397b35d..29900ab 100644
--- a/src/DotNetOpenAuth.OpenId.Provider/Properties/AssemblyInfo.cs
+++ b/src/DotNetOpenAuth.OpenId.Provider/Properties/AssemblyInfo.cs
@@ -7,7 +7,6 @@
 // We DON'T put an AssemblyVersionAttribute in here because it is generated in the build.
 
 using System;
-using System.Diagnostics.Contracts;
 using System.Net;
 using System.Reflection;
 using System.Resources;
@@ -31,8 +30,6 @@ using System.Web.UI;
 // The following GUID is for the ID of the typelib if this project is exposed to COM
 [assembly: Guid("7d73990c-47c0-4256-9f20-a893add9e289")]
 
-[assembly: ContractVerification(true)]
-
 #if StrongNameSigned
 // See comment at top of this file.  We need this so that strong-naming doesn't
 // keep this assembly from being useful to shared host (medium trust) web sites.
diff --git a/src/DotNetOpenAuth.OpenId.Provider/packages.config b/src/DotNetOpenAuth.OpenId.Provider/packages.config
new file mode 100644
index 0000000..10eec89
--- /dev/null
+++ b/src/DotNetOpenAuth.OpenId.Provider/packages.config
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="Validation" version="2.0.0.12319" targetFramework="net40" />
+</packages>
\ No newline at end of file