* Rewrite Auth RPC types using Swift types.
This largely stems from the unsafe casting that occurs. Current state:
all types have been converted, almost no calls using those types have
been converted, ran into an issue with TwitterAuthCredential where it
takes a parameter that's an RPC type, but can't be visible in ObjC. This
may result in an API change unfortunately, or a rethinking of how the
AuthCredential and Providers work.
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Co-authored-by: Ryan Wilson <wilsonryan@google.com>
Paul Beusterien