Google has updated its security restrictions for the OAuth2 stream. They no longer allow native web views to trigger OAuth streams, but want developers to use OS browsers. It looks like your iOS application is still trying to use web browsing for authentication. You need to fix this so that it opens in the OS browser.
Background Information:
This is just my opinion, but there are many applications that began to force their users to use these built-in browsers (Facebook for one). One may wonder how safe they are and what is the best use of a real installed browser. I suspect that is why google has included this for starters.
More information is available on the Google Blog.
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