Challenge 1: Set a Session With Expiration — Possible Solution
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127.0.0.1:6379> SET session:user55 "token-abc123" EX 1800
OK
127.0.0.1:6379> TTL session:user55
(integer) 1798

WHY THIS WORKS AS AN ANSWER
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30 minutes = 1800 seconds, so SET session:user55 "token-abc123" EX 1800
stores the session value AND sets its expiration to 1800 seconds from
now, in a single command — the shorthand this chapter introduced for
combining a write with a TTL instead of needing a separate EXPIRE call
afterward.

TTL session:user55 then reports how many seconds remain before Redis
automatically deletes the key — here, 1798, reflecting the two seconds
that elapsed between setting the key and checking it (a real,
expected artifact of running two commands one after another, not an
error). No manual cleanup code is needed; once this counts down to 0,
Redis removes the session key on its own.