Request header field authtoken is not allowed by Access-Control-Allow-Headers in preflight response

[MidouT]

Hello Community,

Using client.js to access external REST API, I first have to get a “token” from the public server (“https://api.eurecia.com/eurecia/rest/v1/Auth”)
The request header must contain “authToken : myToken”

Code below:

var request = new Request('https://api.eurecia.com/eurecia/rest/v1/Auth', {
  method: 'GET',
  headers: new Headers({
    'Content-Type': 'application/xml',
    "authToken": euriciaAuth
  })
});

fetch(request)
  .then(res => {console.log(res)}
  .then(error => {console.log(error)});

My request go througth the following error:

Thanks,