Fix auth schema
Fix auth schema

- "default" is for serializing data out of the schema, "missing" is for
deserializing, and in this case we want this flag to be True if it's
missing. All the code that actually uses this already fall back to True
if the property is missing, so this doesn't change any functionality, it
just makes it correct.

dgnorth/drift,dgnorth/drift,dgnorth/drift