Using IParamaterInspector for authentication in WCF

Question

Hi I am thinking to use below startegy to secure a WCF service exposed over internet

Use TransportWithMessageCredentials as security mode in webconfig for SSL and message based security. However i do not want to use clientCredentialType="Username" setting for reasons mentioned below

Problem with UserNamePasswordValidator

• Problem in using Custom UserName Password validator is that only user name and password can be validated using this approach. If i need to validate some other parameters send by the client in the request object then this approach does not work (or atleast i am not aware of)

• Client other than .net often face issues in setting clientCredential

1. So instead of using clientCredentialTypeas "UserName" i am thinking of setting the clientCredentialType="None" so that i do not use the authentication support supplied by WCF framework

2. Create a ParamInspetor class derived by IParameterInspector to
   inspect the request parameter, request object will have the username , password and some other details

3. My requestDTO will be derived from a baseRequestDTO having all the
   properties needed for the validation

i can then access the request object in my parameterinspector class at runtime and can then validate the baseRequestDTO

public object BeforeCall(string operationName, object[] inputs)
    { 
for (int index = 0; index < inputs.Length; index++)
          {
              if (index == 0)
              {
                  baseRequestDTO obj = inputs[index] as baseRequestDTO ;
                  if (obj != null))
                  {
                    // Call Authentication service passing baseRequestDTO
                    // validate username,password and other details                                 
                  }

                  break;
               }
           }
}

Is there any issue in this approach? or is there any better approach? want to know if some one else is doing thing differently.