go-twitch/auth/callback.go

package auth

import (
	"fmt"
	"net/http"
)

type CallbackHandler struct {
	client  *Auth
	handler TokenHandler
}

var _ http.Handler = (*CallbackHandler)(nil)

// CallbackHandler returns an http.Handler that handles callback responses
// from the twitch authentication server.
func (c *Auth) CallbackHandler(h TokenHandler) http.Handler {
	return &CallbackHandler{
		client:  c,
		handler: h,
	}
}

// ServeHTTP implements http.Handler.
func (c *CallbackHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	q := r.URL.Query()
	state := q.Get("state")

	if state == "" {
		http.Error(w, "state is empty", http.StatusBadRequest)
		return
	}

	storedState, err := c.client.stateStorage.Get(r)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	if state != storedState {
		http.Error(w, "state mismatch", http.StatusBadRequest)
		return
	}

	if q.Has("error") {
		err := q.Get("error")
		desc := q.Get("error_description")

		errMsg := fmt.Sprintf("%s: %s", err, desc)

		http.Error(w, errMsg, http.StatusBadRequest)
		return
	}

	code := q.Get("code")
	scope := q.Get("scope")
	_ = scope

	token, err := c.client.GetTokenFromCode(r.Context(), code)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	c.handler.Handle(state, token.AccessToken)
}