Implement class for parsing and serializing a admin.system.keys document:
{ _id: <int>, purpose: 'signLogicalTime', key: <20 byte key generated with secure PRNG in BinData>, expiresAt: <LogicalTime, currently Timestamp format> }
class KeysCollectionDocument { public: KeysCollectionDocument(long long keyId, std::string purpose, TimeProofService::Key key, LogicalTime expiresAt); static StatusWith<TypeKeys> fromBSON(const BSONObj& doc); BSONObj toBSON() const; // getter methods };