Cloudflare captcha may prevent refresh token request

[UweTrottmann]

Another person has brought this up at #626, but it looks like this discussions feature should be used instead. So reposting this here:

It appears that Cloudflare may hit requests to oauth/token with a captcha in some situations, breaking the OAuth flow.

In error reports of SeriesGuide I see refresh access token requests (to oauth/token) occasionally returning unexpected data. But I can't tell you what is returned, only that it's not the expected new access token. But as the HTTP status code indicates success, it may very well be a captcha page as that person is suggesting.