thrift: Validate login
thrift: Validate login

This patch validates that a user is correctly logged in (if
authentication is required) for the required verbs.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

raphaelsc/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla,raphaelsc/scylla,avikivity/scylla,kjniemi/scylla,raphaelsc/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla,kjniemi/scylla,duarten/scylla