Improved OAuth errors handling
feature #5 Improved OAuth errors handling (tucksaun)

This PR was squashed before being merged into the 2.x-dev branch (closes #5).

Discussion
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Improved OAuth errors handling

Adaptation regarding https://github.com/sensiolabs/connect/pull/47

@lyrixx Maybe a entry in the doc explaining how displaying authentication errors is now necessary?

Commits
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2d54033 Improved OAuth errors handling