Fetch API cannot load ... No 'Access-Control-Allow-Origin' header - node.js

Question

I got
a rest api deployed on heroku
a react app deployed on heroku
the react app tries to get data from the rest api using whatwg-fetch.
var header = {"Content-Type": "multipart/form-data", 'Origin': 'https://foo.bar', 'Access-Control-Request-Method': 'GET', 'Access-Control-Request-Headers': 'X-Requested-With'};
var options = {method: 'GET', credentials: 'include', headers: header};
fetch('https://myrest.api/foo', options)...
But I can't get any data, it say's
Fetch API cannot load https://foo.bar.
No 'Access-Control-Allow-Origin' header is present on the requested resource.
Origin 'https://foo.bar' is therefore not allowed access.
The response had HTTP status code 403.
If an opaque response serves your needs, set the request's mode to 'no-cors'
to fetch the resource with CORS disabled.
When I try to get the data with curl it works
curl -H "Origin: https://foo.bar" \
-H "Access-Control-Request-Method: GET" \
-H "Access-Control-Request-Headers: X-Requested-With" \
-X GET --verbose https://myrest.api/foo -D header.txt
and the response header (from the curl command)
HTTP/1.1 200
Server: Cowboy
Connection: keep-alive
Access-Control-Allow-Origin: https://foo.bar
Vary: Origin
Access-Control-Allow-Credentials: true
Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked
Date: Fri, 09 Dec 2016 23:52:57 GMT
Via: 1.1 vegur
Cors is enabled in the spring boot application via #CrossOrigin
Thanks in advance
Best Regards

Answer 1

It seems that you are trying to access from one domain https://foo.bar into another domain at https://myrest.api and that is the reason for that error.
You have 2 options:
1) Merge this 2 apps into one single domain on Heruko, React and the Api apps will be under https://foo.bar domain for example and that will work for you.
2) Allow the client app domain at https://foo.bar to access into your api domain at https://myrest.api by adding "Access-Control-Allow-Origin" header into the api app:
app.use(function(req, res, next) {
res.header("Access-Control-Allow-Origin", "*");
next();
});