The 'Access-Control-Allow-Origin' header contains multiple values ' ', '*' - asp.net-web-api

Question

I am working with ASP.NET WEB Api, and I'm using authentication Token, Internet Explorer generates the Token string:
But using any other browser shows the following error :
The 'Access-Control-Allow-Origin' header contains multiple values
AJAX code:
function ObtenerToken(user, password) {
var data = { username: user, password: password, grant_type: "password" }
$.ajax({
url: 'http://localhost:50196/Token',
method: "post",
data: data,
contentType: "application/json",
error: function (e) {
alert('Hubo un error al intentar autenticar al usuario.');
console.log(e);
},
success: function (response) {
var token = response.access_token;
alert(token);
}
});
}
The file Startup.Auth.cs i have set the following
app.UseCors(CorsOptions.AllowAll);
In WebApiConfig.cs
EnableCorsAttribute cors = new EnableCorsAttribute("*", "*", "*");
config.EnableCors(cors);
And in class Controller:
[EnableCors(origins: "*", headers: "*", methods: "*")]
public class UsuariosController : ApiController
{

Answer 1

I'm pretty sure this is because you're adding the Access-Control-Allow-Origin header in all three of those places. You should enable CORS in Startup.Auth.cs, in WebApiConfig.cs, OR in the controller - one of these places, not all three.

Answer 2

You need to enable cors.
public void Configuration(IAppBuilder app)
{
HttpConfiguration config = new HttpConfiguration();
app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);
ConfigureOAuth(app);
WebApiConfig.Register(config);
// Make sure this line is called before ConfigureAuth(app),
// app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);
app.UseWebApi(config);
}