Operation Contract - Parameter not popuplated

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C#

.NET

WCF

.NET4

I have a WCF service with the below service\operation\data contracts.

namespace Enrollment
   {
       [ServiceContract(Namespace = "http://docs.oasis-open.org/ws-sx/ws-trust/200512")]
       public interface wstep
       {

           [OperationContract(Action = "http://schemas.microsoft.com/windows/pki/2009/01/enrollment/RST/wstep", Name = "RequestSecurityToken")]
           RequestSecurityTokenResponseCollection RequestSecurityToken(string TokenType, string RequestType, BinarySecurityToken binarySecurityToken, AdditionalContext additionalContext);

       }

   [DataContract(Namespace = "http://schemas.xmlsoap.org/ws/2006/12/authorization")]
       public class AdditionalContext
       {
           [DataMember]
           public List<ContextItem> contextItem { get; set; }
       }

   [DataContract(Namespace = "http://schemas.xmlsoap.org/ws/2006/12/authorization")]
       public class ContextItem
       {
           [DataMember]
           public string Name { get; set; }

           [DataMember(Name="Value")]
           public object Item { get; set; }

       }

       [XmlRoot("BinarySecurityToken")]
       [DataContract(Namespace = "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd", Name = "BinarySecurityToken")]
       public class BinarySecurityToken
       {
           [XmlAttribute("ValueType")]
           [DataMember(Name = "ValueType",Order=1)]
           public string ValueType { get; set; }

           [XmlAttribute("EncodingType")]
           [DataMember(Name = "EncodingType", Order = 2)]
           public string EncodingType { get; set; }
       }
   }

However, I see that the client connects to the service but the last two parameters of the Operation - BinarySecurityToken and AdditionalContext are null when I check their values in the service. I have traced the client request, and I see the values are sent by the client correctly. The below mentioned is the SOAP body.

<s:Body>
           <wst:RequestSecurityToken>
               <wst:TokenType>http://schemas.microsoft.com/5.0.0.0/ConfigurationManager/Enrollment/DeviceEnrollmentToken</wst:TokenType>
               <wst:RequestType>http://docs.oasis-open.org/ws-sx/ws-trust/200512/Issue</wst:RequestType>
               <wsse:BinarySecurityToken ValueType="http://schemas.microsoft.com/windows/pki/2009/01/enrollment#PKCS10" EncodingType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd#base64binary">MIICcTCCAV0CAQAwMDEuMCwGA1UEAxMlQj=</wsse:BinarySecurityToken>
               <ac:AdditionalContext xmlns="http://schemas.xmlsoap.org/ws/2006/12/authorization">
                   <ac:ContextItem Name="DeviceType">
                       <ac:Value>MyDevice</ac:Value>
                   </ac:ContextItem>
                   <ac:ContextItem Name="ApplicationVersion">
                       <ac:Value>18.10.6603.101</ac:Value>
                   </ac:ContextItem>
               </ac:AdditionalContext>
           </wst:RequestSecurityToken>
       </s:Body>

The first two parameters are showing up correctly. No idea what is going on.