Wrong credentials in REST fetch with multiple users per session - reactjs

Question

I have a webapp (using react, redux) that fetchs data via REST. Everything works fine as long as I'm only logging in one user per session. If I'm logging in multiple users at once using the same browser, in the BE (java with spring) the wrong principal (always the principal for the latest logged in user) is received.
How I can send the correct credentials for each user?
FE:
public restPost(url: string, request: any): Rx.Observable<any> {
return Rx.Observable.create(
(observer: Rx.Observer<any>) => {
fetch(url, {
method: 'POST',
mode: 'cors',
credentials: 'include',
headers: {
Accept: 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify(request)
}).then((response: Response) => {
// handle response
})
.catch(error => observer.error(error));
}
);
}
BE:
#RequestMapping(value="/test", method = RequestMethod.POST)
#CrossOrigin(origins = "*")
public ResponseEntity<Test> test(#RequestBody TestRequest testReq, HttpServletResponse response, #AuthenticationPrincipal Principal principal) {
// at this point the principal.getName() has the name of the latest logged in user
// return the response
}

Answer 1

My solution (only working because I have also have a websocket connection):
added a bearer token to the REST headers in the FE:
headers: {
Accept: 'application/json',
'Content-Type': 'application/json',
Authorization: header ? ('Bearer ' + header.token) : ''
}
In the BE I saved a map with token to principals which I could then access for REST messages