NIP-FA fixed the assertion lifetime at 300 seconds. That limit belongs
to the adapter operator: the relay already enforces each issuer's
configured `maximum_assertion_age`.
This changes the `expires_at` paragraph to:
- make the lifetime the adapter operator's policy;
- keep the rule that `exp` cannot be later than the adapter session's
expiry;
- require the lifetime to stay within the `maximum_assertion_age` the
relay accepts for the issuer;
- replace "Clients MAY refuse … more than 300 seconds" with a rule that
clients must not refuse an assertion for its lifetime alone;
- state that the lifetime bounds how long a revoked key can keep
reconnecting after a relay restart.
NIP-FI and the other NIPs have no fixed 5-minute assertion rule, so they
are unchanged.
Signed-off-by: Will Pfleger <wpfleger@block.xyz>
f1ce1c5d47