Top 20 NuGet oauth2 Packages

Helper library for claims based identity & access control in OWIN/Katana based applications.
Plugin for adding WS-Federation Identity Provider capabilities to IdentityServer3
Thinktecture IdentityServer Core Libraries for Re-Hosting (for IdentityServer v2)
Fitbit API client for .NET
This package adds support for integrated Windows authentication to IdentityServer.
A set of e-mail components which implement IMAP, SMTP, POP3, Exchange Web Services, SSL/TLS support, parsing and building MIME and S/MIME messages, Outlook .MSG and .PST conversions, mail merge over database, OAuth 2.0, DNS MX lookup, e-mail address validation, parsing winmail.dat, bounced messages ...
Claims-based OAuth2 integration
SimpleAuthentication is a ASP.NET library that makes it really simple to for developers to add Social Authentication code to an ASP.NET application.
Delegation Handler based Authentication Framework for ASP.NET Web API v2.
OWIN middleware for validating OAuth2 and OpenID Connect scope claims.
Scope-based Authorization for Web API v2.
An Umbraco plugin to add an OAuth API endpoint to allow authenticated Members/Users via OAuth
Client helper for OAuth2 2-legged flows with client secret and JWT client assertion support and token caching
The Relativity OAuth2 API client .NET package.
Entity Framework Persistence Layer for the IdentityServer3 WS-Federation Plugin
Helper library for claims-based identity, System.IdentityModel, JSON Web Tokens, OAuth 2.0 and OpenID Connect client
Helper extensions to configure Swashbuckle Swagger and Swagger UI to use OAuth implicit grant with Azure AD b2c
ASP.NET 5 Middleware for validating scope claims
A set of Windows Forms dialogs for DeviantArt OAuth2 flow
NHibernate persistence layer for IdentityServer4.