MVC 5 App via Facebook OAuth2 Login (sign-on) issue

Today's example of using the MVC 5 app to sign in via Google, Twitter, Linkedin and Facebook is a primer on the ASP, and the following issues have been found in the process, and specific solutions have been found through Google. .

The problem is to do the corresponding Facebook app and ASP, press Ctrol + F5 run the site, through the Facebook input login account login, the page red throw exception, the exception information as follows:

System.NullReferenceException:Object reference not set to a instance of an Object.

Cause of the problem: Facebook OAuth 2.0 is not enabled.

Middleware that enables a application to support Facebook's OAuth 2.0 authentication workflow.

Workaround:

Install Facebook OAuth 2.0 via PMC

To install Microsoft.Owin.Security.Facebook, run the following command in the package Manager Console

PM> Install-Package Microsoft.Owin.Security.Facebook -Version 2.1.0