I am dealing with the same problem written in previous article ( Loginned, but passport not deserializing )

Trial 2) Setting CORS in Server

link1 ) https://ko.javascript.info/fetch-crossorigin
link2 ) http://guswnsxodlf.github.io/enable-CORS-on-express

Let's See what CORS is

CORS = Cross-Origin-Resourse-Sharing

* What is Origin(출처)

one url such as (www.google.com) seems like one componenent but is is comprised of multiple components

it's not included in image, but port such as ':80', ':43' is also included

That is, above url includes all the basic elements to reach the location of the server( If the port is empty or not given, port 80 is assumed )

You can simply check where the application is running

console.log(location.origin);

Okay, Now I know what the 'origin' is,
Then, How do we decide whether origin is same or not

It's very simple, among the elements of url,
if 3 things
1) Scheme
2) Host
3) Port

For Example,
" https://evan-moon.github.io:80"
1) Scheme : https://
2) Host : evan-moon.github.io
3) Port :80

It is regarded as same origin, even if other elements differ

Anyway...

Even if It does not seem to be related with cors issue, since I am using the same origin,
I added below code to main server code

app.use(cors({credentials: true, origin: '~'}));

What is Restful Api, and why is it related with CORS

CORS란 무엇인가
CORS란 Cross Origin Resource Sharing의 약자로, 현재 도메인과 다른 도메인으로 리소스가 요청될 경우를 말한다. 예를 들어, 도메인 http://A.com 에서 읽어온 HTML페이지에서 다른 도메인 http://B.com/image.jpg를 요청하는 경우를 말한다. 이런 경우에 해당 리소스는 cross-origin HTTP 요청에 의해 요청된다. 보안 상의 이유로, 브라우저는 CORS를 제한하고 있다.

하지만 SPA(Single Page Application)의 경우에는, RESTful API를 기반으로 비동기 네트워크 통신을 하기 때문에 API 서버와 웹 페이지 서버가 다를 수 있다. 이런 경우에 API 서버로 요청을 할 시에 CORS 제한이 걸리게 된다.

Trial 3) 304 Status Code

When I checked the status code, when problemn occurred,
I found out that status code is 304

What is 3xx ?
3xx: Redirection - Further action must be taken in order to complete the request
( 리다이렉션 - 요청이 완수되기 위해서 추가적인 동작이 이뤄져야 함 )

That is, it occurs when the requested result is not different from pre-request result.

That is , it's because it's using cached page

link related with cache : https://cyberx.tistory.com/9

Trial 4) Going Through the basic process of the entire passport js

link 1 : https://github.com/jaredhanson/passport/issues/482