Major Description
Rather than add a new thrift object for each possible type of authentication token (I saw 3 created for ACCUMULO-259), we should just make our token interface extend Writable, and use a single thrift object to carry the user principal, token type, and binary serialized token, in our RPC calls.
I think the now deprecated "AuthInfo" object was acceptable for this purpose, though with different fields and behavior than before. However, since that object was in the public API in 1.4.x, it needs to remain as is, until it is phased out of the public API. A similar object, (perhaps 'Authentication'), containing the user principal, token type, and binary serialized token, should be created for this purpose instead, for the RPC calls.