The 'Access-Control-Allow-Origin' header contains multiple values

I am facing this problem when i send any request to any method

here is my startup.ts

public void Configuration(IAppBuilder app)

{

// For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=316888

HttpConfiguration config = new HttpConfiguration();

app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);

EnableCorsAttribute cors = new EnableCorsAttribute("*", "*", "*");

var provider = new Myauthenticationserverprovider();

OAuthAuthorizationServerOptions options = new OAuthAuthorizationServerOptions

{

AllowInsecureHttp = true,

TokenEndpointPath = new PathString("/token"),

AccessTokenExpireTimeSpan = TimeSpan.FromDays(1),

Provider=provider

};

app.UseOAuthAuthorizationServer(options);

app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());

config.EnableCors(cors);

WebApiConfig.Register(config);

}

i am able to access the token but problem with passing token in header