Response cookie not being set in browser storage

Question

I'm generating a JWT and sending back to the user as a cookie. I see the response cookie in the network, but the brower isn't storing the cookie, which effectively breaks all my authentication/authorization.

    w.Header().Add("Access-Control-Allow-Origin", "*")
    w.Header().Add("Access-Control-Allow-Credentials", "true")
    w.Header().Add("Access-Control-Allow-Headers", "*")

    w.Header().Set("Content-Type", "application/json")
    http.SetCookie(w, &http.Cookie{
        Name:   "auth_token",
        Value:  jwt,
        MaxAge: 3600,
        Path:   "/",
    })
    json.NewEncoder(w).Encode(fmt.Sprintf("{'result': '%s'}", jwt))

I should mention that I'm running a UI server on port 3000 and web server on port 8080. I assume the mismatched ports on 127.0.0.1 is causing this to fail, however, I don't know a workaround.