Top 20 NuGet Security Packages

Provider Agnostic OAuth authentication with External Providers
Database interfaces and entities used by Glipho.OAuth.Providers.
Portable Client Library and HttpClient based OAuth library, including all platform(for PCL).
A simplified interface for dealing with Evernote via OAuth (Asynchronously or Synchronously)
Allows you to perform user authentication via DigitalOcean, Facebook, Foursquare, GitHub, Google, Instagram, LinkedIn, MailRu, Odnoklassniki, Salesforce, Twitter, VK (Vkontakte), Windows Live, Yandex,QQ,Weibo,Baidu,JD,Kaixin001,360,renren,taobao just in two method calls.
Third Party Login Plug-In for .NET,include Tencent's QQ,Sina's weibo,Baidu's Account
Implementation of the data sources provided by Windows AppStudio. This library enable access to diferent data source like RSS, Bing, Facebook, Flickr, Instagram, Twitter and YouTube.
Partial .NET implementation of OAuth 2.0 RFC 6749
Provides a default starting point for setting up a new JWT OAuth server which includes Its.Configuration and Its.Log with a set of classes that preconfigure numerous defaults. All you have to do is provide service setup and your actual authentication (one method implementation).
Azure OAuth2 helper to obtain acess token
Allows you to perform user authentication via DigitalOcean, Facebook, Foursquare, GitHub, Google, Instagram, LinkedIn, MailRu, Odnoklassniki, Salesforce, Twitter, VK (Vkontakte), Windows Live, Yandex just in two method calls.
ASP.NET 4.x Resource Server components for consuming OAuth tokens genetrated by an Authorization Server based on OAuth.AspNet.AuthServer
Implementation of Spotify authorization flows for UWP apps.
Implementation of Spotify authorization flows for ASP.NET Core apps.
EasyOAuth Framework is an OAuth-compliant application framework for application needs to integrate APIs for service providers require OAuth authentication.
TwitterDoodle is fully asynchronous .NET Twitter client which embraces Task Parallel Library from top to bottom
OAuth provider for the Bungie.net API using OWIN
Authenticate against the Wordpress API without OAuth, and make requests to its REST API. You will need a wordpress username, password, and blog ID. Get your Blog ID by going to https://developer.wordpress.com/docs/api/console/ then Login and search /me/sites or /sites/hello.wordpress.com
Owin Middleware to handle authenticating with Azure AD
OAuth2 server implementation.