URI HTTPS request

It sounds like you're making a client-side app, so the implicit flow using a localhost redirect URI is a reasonable approach. As you saw though, by default there isn't anything being served at localhost, so you're getting that error. You can just grab the access token anyway, but you may want to run a small web server to receive it in order to polish the experience. (Alternatively, you can use an actual web address, such as this one that we provide for purposes like this: https://www.dropbox.com/1/oauth2/redirect_receiver )

Also, to clarify, the client ID is just your app key, which should just be embedded in your app for use by all users of your app to start the app authorization flow. Only the resulting access token is user-specific. You can store and re-use the resulting access token for each user so that they don't have to repeatedly go through that flow.