Object reference not set to an instance of an object at System.Web.Security.FormsAuthentication.SetAuthCookie

Question

I have created WCF project hosted with MVC and would like to implement WebSecurity.Login(string,string) which is as follows

public bool LoginService(string UserName, string Password)
    {
        bool answer = false;
        try
        {

            App.AppInitialize();
            bool x = Membership.ValidateUser(UserName, Password);
               Console.WriteLine(x.ToString());
                if (x)
                {
                    SetAuthCookie(UserName, false);
                    answer = true;
                }
                else
                {
                    answer = false;
                }


            return answer;
        }
        catch (Exception e)
        {
            Console.WriteLine(e.StackTrace);
            return answer;

        }

    }

And I have following config in App.Config(of WCF project which is service class) but not added in Web.Config(of MVC)

<system.web>
<!-- Configure the Sql Membership Provider -->
<authentication mode="Forms" />
<membership defaultProvider="SqlMembershipProvider" userIsOnlineTimeWindow="15">
  <providers>
    <clear />
    <add
      name="SqlMembershipProvider"
      type="System.Web.Security.SqlMembershipProvider"
      connectionStringName="ABCEntities"
      applicationName="XXX.WCF"
      enablePasswordRetrieval="false"
      enablePasswordReset="true"
      requiresQuestionAndAnswer="false"
      requiresUniqueEmail="false"
      passwordFormat="Hashed"/>
  </providers>
</membership>
<compilation debug="true" />    

Every time I test on WCF test client I get the false in return and when I track the stacktrace I get following response

        StackTrace  "   at System.Web.Security.FormsAuthentication.SetAuthCookie(String userName, Boolean createPersistentCookie, String strCookiePath)\r\n   at System.Web.Security.FormsAuthentication.SetAuthCookie(String userName, Boolean createPersistentCookie)

and

TargetSite  {Void SetAuthCookie(System.String, Boolean, System.String)} System.Reflection.MethodBase {System.Reflection.RuntimeMethodInfo}

I have already spent hours and hours to figure it out and had a look at Why am I getting a NullReferenceException from Membership.GetCurrentUserName? and also in https://msdn.microsoft.com/en-us/library/ms731049.aspx

Little bit of helpful question was asked at Authentication to a WCF service not maintained using SetAuthCookie and a full .net client but works with silverlight

but was unable to sort it out. Thank you in advance if you could provide some code snippet along with explannation.