Authenticating Telerik users in separate web application fro

I want to allow our users from our Sitefinity 8.2-driven site to be able to log into a separate web application using their Sitefinity credentials.  

For testing, I've added the membership provider from our Sitefinity web.config to the new web app's web.config:

<membership defaultProvider="Default">
      <providers>
        <clear />
        <add name="Default" type="Telerik.Sitefinity.Security.Data.SitefinityMembershipProvider, Telerik.Sitefinity" />
        </providers>
    </membership>

I have also referenced the Telerik.Sitefinity library from 8.2, and added 

"using Telerik.Sitefinity.Security" to the separate web app's code behind

so that I could authenticate the user by using

var validate = SecurityManager.AuthenticateUser(UserManager.GetDefaultProviderName(), login2.UserName, login2.Password, false);

However, whenever I do that I get an Object referene not set to an instance of an object error.  I'm assuming that the UserManager.GetDefaultProviderName() is not being referenced correctly.  

I'm also assuming that the binding to the Sitefinity 8.2's SQL database which is named "NewSitefinity" might be to blame as well.  

The details for that in the <connectionStrings>

<add name="Sitefinity" connectionString="Data Source=SQL1;Initial Catalog=NewSitefinity;Integrated Security=True" providerName="System.Data.SqlClient"/>

Any suggestions to what I'm missing and what other requirements I may need to include so that this application can authenticate the user in our parent Sitefinity 8.2 site?   Thank you!

I've attached my stack trace: