lib/oauthutil: fix redirect URL mismatch errors - fixes #8351

In this commit we introduced support for client credentials flow:

65012beea4b93b7f lib/oauthutil: add support for OAuth client credential flow

This involved re-organising the oauth credentials.

Unfortunately a small error was made which used a fixed redirect URL
rather than the one configured for the backend.

This caused the box backend oauth flow not to work properly with
redirect_uri_mismatch errors.

These backends were using the wrong redirect URL and will likely be
affected, though it is possible the backends have workarounds.

- box
- drive
- googlecloudstorage
- googlephotos
- hidrive
- pikpak
- premiumizeme
- sharefile
- yandex

lib/oauthutil/oauthutil.go

@@ -108,7 +108,7 @@ func (conf *Config) MakeOauth2Config() *oauth2.Config {
 	return &oauth2.Config{
 		ClientID:     conf.ClientID,
 		ClientSecret: conf.ClientSecret,
-		RedirectURL:  RedirectLocalhostURL,
+		RedirectURL:  conf.RedirectURL,
 		Scopes:       conf.Scopes,
 		Endpoint: oauth2.Endpoint{
 			AuthURL:   conf.AuthURL,