public interface IService1 : MyExternalService

public class Service1 : IService1
        {
            public string GetData(int value)
            {
                return string.Format("You entered: {0}", value);
            }

            public string ExternalMethod1(string a, string b)
            {
                throw new NotImplementedException();
            }

//etc

<configuration>

  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
  </appSettings>
  <system.web>
    <compilation debug="true" targetFramework="4.5" />
    <httpRuntime targetFramework="4.5"/>
  </system.web>
  <system.serviceModel>
    <bindings>
      <wsHttpBinding>
        <binding name="WSHttpBinding_IExternalService">
          <security>
            <message clientCredentialType="Certificate" />
          </security>
        </binding>
        <binding name="WSHttpBinding_IExternalService1">
          <security>
            <message clientCredentialType="Certificate" negotiateServiceCredential="false"
              algorithmSuite="Basic128" establishSecurityContext="false" />
          </security>
        </binding>
      </wsHttpBinding>
    </bindings>
    <client>
      <endpoint address="http://service.com/ExternalService/ExternalService.svc"
        binding="wsHttpBinding" bindingConfiguration="WSHttpBinding_IExternalService"
        contract="ExternalService.IExternalService" name="WSHttpBinding_IExternalService">
        <identity>
          <dns value="service.com" />
        </identity>
      </endpoint>
      <endpoint address="http://service.com/ExternalService/ExternalService.svc/Java"
        binding="wsHttpBinding" bindingConfiguration="WSHttpBinding_IExternalService1"
        contract="ExternalService.IExternalService" name="WSHttpBinding_IExternalService1">
        <identity>
          <dns value="service.com" />
        </identity>
      </endpoint>
    </client>
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <!-- To avoid disclosing metadata information, set the values below to false before deployment -->
          <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <protocolMapping>
        <add binding="basicHttpsBinding" scheme="https" />
    </protocolMapping>
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
    <!--
        To browse web app root directory during debugging, set the value below to true.
        Set to false before deployment to avoid disclosing web app folder information.
      -->
    <directoryBrowse enabled="true"/>
  </system.webServer>

</configuration>

<services>
   <service name="MyService.MyService" behaviorConfiguration="metadataBehavior">
      <endpoint
          address="http://localhost/MyService.svc"
          binding="customBinding" bindingConfiguration="jsonpBinding"
          behaviorConfiguration="MyService.MyService"
          contract="MyService.IMyService"/>
      <endpoint
          address="mex"
          binding="mexHttpBinding"
          contract="IMetadataExchange"/>
   </service>
</services>