Fix Apple IdentityToken conversion

[ttermeer-reboundcg]

Fix for #880 and possibly #830

My knowledge is limited for Objective-C so any feedback is welcomed. Solution taken from stackoverflow

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[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
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[morganchen12]

Thanks @ttermeer-reboundcg!

[morganchen12]

It seems you've signed the CLA with an email that's different than the one in your commit. Can you re-sign the CLA with the correct email?

[ttermeer-reboundcg]

@morganchen12 I verified. Commit is under the right email address but the CLA just got approved 6 hours ago.

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[morganchen12]

Thanks!