title: Startup.cs - The path in 'value' must start with '/'
body: <p>I have created a new .NET Core MVC application in Visual Studio 2017 and enabled multi-tenant authentication. <br/>
  I've completed the configuration (ClientId, Authority, etc) but when I debug the application there is an exception in the Startup.cs, specifically the <code>app.useOpenIdConnectAuthentication</code> method.</p>
  
  <p>The exception given is</p>
  
  <blockquote>
    <p>System.ArgumentException: The path in 'value' must start with '/'.</p>
  </blockquote>
  
  <p>I'm a bit of a novice when it comes to C# and .NET Core, so I'm not sure whether I'm missing something obvious. The main sticking point is what the debugger is referring to with the parameter 'value' as I can't see any mention of it in the code. There are no changes beyond the default template generated by visual studio, other than adding the configuration items to the appsettings.json.</p>