Top 20 NuGet authentication Packages

Windows Authentication for Azure (kind of)
Hawk Http Authentication for RestSharp
Hawk Http Authentication for ServiceStack
Simple Token and Users Authentication and Authorization Bootstrap for WebAPI applications. Provided with 'TokenAuthApiController' which has built-in support for Login and Logout (cookies-based) and automatic token parsing and authenticating (inside query strings, form data or cookies). Visit the Pro...
A better implementation of ExtendedMembershipProvider with support for legacy MembershipProvider APIs.
Library for connecting your application to UserApp.
A DotNetOpenAuth client for logging in to OSChina using OAuth2.
Token based auth for WebApi.
Owin authentication handler for Obsidian Portal
PerFieldAuth for ServiceStack allows for defining authentication roles required for the specific DTO fields to be accessible
A simple login policy for Glimpse to protect your site in production
A C# port of chef's mixlib-authentication
Simple ASP.NET Core authentication and identity provider. Valid users are specified in a simple configuration file. Please refer to the project site at http://dan.cx/projects/SimpleIdentity for full installation instructions, usage examples, and sample code.
Services for managing and hashing passwords.
Build claims for authenticated user and construct a user object from claims.
A C# library to provide Steam Mobile Authenticator functionality
WebApi.BasicAuth provides HTTP Basic Authentication with usernames and passwords stored in Web.config.