Can't get "Set-Cookie" header from response in signin route

[DevDugg]

I can't get Set-Cookie header for response, it generates this error:

I tried different casings like "set-cookie", "Set-COOKIE" and etc., the result is the same.

I tried doing console.log(response.headers), and it turns out that "Set-Cookie" is not among the headers at all:

Though, in Postman everything is working correctly without any issues.

I heard supertest doesn't work very well with cookies.
Is this an issue caused by supertest itself? What can I do to tackle the issue?

Any help is appreciated.

Source code