💡 INF level log after successful token retrieval

## Describe the feature you'd like
When the user is redirected to a browser to complete authentication, there is no immediate STDOUT INF log that indicates whether a token was retrieved successfully or not.


This limits the automation of cloudflared as there's no way to know if the connection was actually auth'd or not.

## Describe alternatives you've considered
At the moment I just use an arbitrary sleep to guess when it might have been approved.

I have seen the following pop up after some time (Windows) but it doesn't appear until a few minutes after. Perhaps a log flushing issue?

## Additional context