Nancy Owin Authentication

gistfile1.cs

public class OwinAuthentication
{
    public static void Enable(IPipelines pipelines, OwinAuthenticationConfiguration configuration)
    {
        if (pipelines == null) throw new ArgumentNullException("pipelines");
        if (configuration == null) throw new ArgumentNullException("configuration");


        pipelines.BeforeRequest.AddItemToStartOfPipeline(GetLoadAuthenticationHook(configuration));
    }

    private static Func<NancyContext, Response> GetLoadAuthenticationHook(OwinAuthenticationConfiguration configuration)
    {
        if (configuration == null) throw new ArgumentNullException("configuration");

        return context =>
        {
            var userGuid = GetUserIdFromOwinContext(context, configuration);

            if (userGuid != Guid.Empty)
            {
                context.CurrentUser = configuration.UserMapper.GetUserFromIdentifier(userGuid, context);
            }

            return null;
        };
    }

    private static Guid GetUserIdFromOwinContext(NancyContext context, OwinAuthenticationConfiguration configuration)
    {
        if (context == null) throw new ArgumentNullException("context");
        if (configuration == null) throw new ArgumentNullException("configuration");

        var env = TryGetFromDictionary<IDictionary<string, object>>(context.Items, NancyOwinHost.RequestEnvironmentKey);
        
        if (env == null) throw new ArgumentNullException("context");
        
        var owinContext = new OwinContext(env);

        if (owinContext.Authentication.User == null)
        {
            return Guid.Empty;
        }

        var claim = owinContext.Authentication.User.Claims.FirstOrDefault(x => x.Type == configuration.ClaimType);

        if (claim == null)
        {
            return Guid.Empty;
        }

        Guid userId;

        if (Guid.TryParse(claim.Value, out userId))
        {
            return userId;
        }

        return Guid.Empty;
    }


    private static T TryGetFromDictionary<T>(IDictionary<string, object> env, string key)
    {
        object value;
        if (env.TryGetValue(key, out value))
        {
            return (T)value;
        }

        return default(T);
    }
}

public class OwinAuthenticationConfiguration
{
    public IUserMapper UserMapper { get; set; }
    public string ClaimType { get; set; }
}

public interface IUserMapper
{
    IUserIdentity GetUserFromIdentifier(Guid userGuid, NancyContext context);
}