DotNetOpenAuth is an open source library for OpenID 1.1 and 2.0 supporting OAuth 1.0, 1.1, 2.0 as Consumer and Service Provider.
DotNetOpenAuth is a free and open source library and is available from DotNetOpenAuth.net. It features support for OpenID 1.1 and 2.0 Relying Parties and Providers, OAuth 1.0 & 1.1 Consumers and Service Providers, OAuth 2.0 Clients, Resource Servers and Authorization Servers, and Information Card relying parties.
It was formerly knows as DotNetOpenId, but was renamed when it added OAuth and InfoCard support.
Please use this tag instead of the older "dotnetopenid" tag.
Installation
You can install the library most easily using its NuGet package.