public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseIdentityServerBearerTokenAuthentication(new IdentityServerBearerTokenAuthenticationOptions
        {
            Authority = ConfigurationManager.AppSettings["Authority"],
            RequiredScopes = new[] { "api" }
        });
    }
}

var claims = ((ClaimsIdentity)p.Identity).Claims;
        var roleClaim = claims.Where(i => i.Type == "client_role").FirstOrDefault();
if (roleClaim == null)
{
   return null;
}

private static TokenResponse GetToken()
{
    var client = new OAuth2Client(new Uri(IdentityServerUri), clientId,clientScope);
    return client.RequestClientCredentialsAsync("scope").Result;
 }

var client = new HttpClient();
var tokenResponse = GetToken();
client.SetBearerToken(tokenResponse.AccessToken);
var result = client.GetStringAsync(requestUri).Result;