Chunk server: implement chunk access / security with write append by setting and communicating in the synchronous replication chain the chunk server and chunk access tokens. Add extra validation for tokens with write id subject, by ensuring that such tokens can not be used for any other operations but chunk write operations. Declare write id allocation failure if the operation has chunk access token with write id in the chunk access token subject. Fix chunk server clear text allowed flag setting in write related rpcs when forwarding on write slave, by using the corresponding bit from the chunk access token received from upstream server in the synchronous replication chain. Fix typo in the chunk server access response "Access-time" field resulting in the client requesting access tokens with every write related rpc.
Client lib: fix chunk server access key decryption error condition check. Ensure that chunk server and chunk access time lifetime fields are parsed as 64 bit integers. Write append with security / authentication on started working with synchronous replication chain depth 2. Append status recovery with write slaves and security on isn't implemented yet.