GoogleOAuth2AuthenticationProvider AccessToken not getting validated

I am using the GoogleOAuth2AuthenticationOptions class for authentication in my MVC5 Web App (SPA Template).  Given below is the code

var g = new GoogleOAuth2AuthenticationOptions
            {
                ClientId = "clientid",
                ClientSecret = "secret",
                //CallbackPath="",
                Provider = new GoogleOAuth2AuthenticationProvider
                {
                    OnAuthenticated = async ctx =>
                        {
                            ctx.Identity.AddClaim(new Claim("urn:tokens:google:accesstoken", ctx.AccessToken));
                        }
                }
            };
            // restrict the retrieved information to just signin information
            g.Scope.Add("openid");
            app.UseGoogleAuthentication(g);

The token I get is something like this

ya29.LgAibra6cNLEKCEAAADLJxUOviZRgv9JSm-jrB-lNp16nomUijNrVAbcdDkI60Vg-A9yjFN4abcd_C8b4

I am using this token in subsequent calls to a MVC WebAPI which uses OAuthBearerTokens for security.  I send the access token through the header in my WebAPI call from my MVC Web app

app.UseOAuthBearerTokens(OAuthOptions);       

The javascript generated on the client contains a much larger token which works with my MVC WebAPI.  Does anyone know how to fix this?