Going through the link you sent me I saw my comments from last July.
Unfortunately, the resolution of this long known keychain issue hasn't
progressed much. Besides with the limitation of closed source lib :( it is
difficult to know the details of the issue. Even in the cookbook demo app I
had to backup and use UntrustedMemoryOAuth2Session .
What I would recommend is going another route and implement you own secure
OAuth2Session storage using encryption lib . The problem is that when
you encrypt you need ti input a password which a usability trade-off to
have tokens stored in a secure encrypted version. You could use TouchID 
to make it easy.
On 3 February 2016 at 20:44, Michael Doo <michael(a)410labs.com> wrote:
In the Aerogear iOS OAuth2 library, getting an error when app enters
foreground after period of being in background. Specifically, in
TrustedPersistantOAuth2Session.swift, KeyChainWrap.read() is (very)
occasionally throwing errSecMissingEntitlement and then throwing the user
over to Safari for authentication. This is a show stopper bug for our app.
Some discussion of the topic and acknowledgement by Apple here:
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