Web API Redirection 2 from GetExternalLogin

Question

Web API Redirection 2 from GetExternalLogin

I am trying to configure a new configuration for Web API 2 using Identity and external authentication providers. My scenario is two asp.net applications, a Web API as a data provider, and MVC as a data consumer. I call the GetExternalLogins method in the Web API and, based on the returned list, generate a series of links in my MVC application. Whenever the user clicks on any of them, it is redirected to the GetExternalLogin method:

    // GET api/Account/ExternalLogin
    [OverrideAuthentication]
    [HostAuthentication(DefaultAuthenticationTypes.ExternalCookie)]
    [AllowAnonymous]
    [Route("ExternalLogin", Name = "ExternalLogin")]
    public async Task<IHttpActionResult> GetExternalLogin(string provider, string sender, string error = null)
    {
        if (error != null)
        {
            return Redirect(Url.Content("~/") + "#error=" + Uri.EscapeDataString(error));
        }

        if (!User.Identity.IsAuthenticated)
        {
            return new ChallengeResult(provider, this);
        }

        ExternalLoginData externalLogin = ExternalLoginData.FromIdentity(User.Identity as ClaimsIdentity);

        if (externalLogin == null)
        {
            return InternalServerError();
        }

        if (externalLogin.LoginProvider != provider)
        {
            Authentication.SignOut(DefaultAuthenticationTypes.ExternalCookie);
            return new ChallengeResult(provider, this);
        }

        var user = await UserManager.FindAsync(new UserLoginInfo(externalLogin.LoginProvider,
            externalLogin.ProviderKey));

        bool hasRegistered = user != null;

        if (hasRegistered)
        {
            Authentication.SignOut(DefaultAuthenticationTypes.ExternalCookie);
            ClaimsIdentity oAuthIdentity = await UserManager.CreateIdentityAsync(user,
                OAuthDefaults.AuthenticationType);
            ClaimsIdentity cookieIdentity = await UserManager.CreateIdentityAsync(user,
                CookieAuthenticationDefaults.AuthenticationType);
            AuthenticationProperties properties = ApplicationOAuthProvider.CreateProperties(user.UserName);
            Authentication.SignIn(properties, oAuthIdentity, cookieIdentity);
        }
        else
        {
            IEnumerable<Claim> claims = externalLogin.GetClaims();
            ClaimsIdentity identity = new ClaimsIdentity(claims, OAuthDefaults.AuthenticationType);
            Authentication.SignIn(identity);
        }

        var test = Ok();

        return Ok();
    }