Hello Alex,
We stumbled upon a difference between iOS 4 and iOS 5 regarding the handling of redirect URLs.
On iOS 4 a redirected request still contains the Authorized header field and one manually had to remove it if the request was redirected to a different domain or from HTTPS to HTTP.
In iOS 5 the Authorized header no get's removed by default, meaning that one needs to re-add it.
We updated the OAuth2 library and pushed a commit with the updated reference to github.
Please check if that fixes the issue you're having.
Except of this issue we're using the API wrapper on iOS 5 already.
Thanks,
Ullrich
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Ullrich Schäfer
iOS Team, SoundCloud