Blind key rotation and stale duration for profiles

See https://blog.dereferenced.org/the-case-for-blind-key-rotation

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

CHANGELOG.md

@@ -21,6 +21,11 @@ Also make sure to remove the `EnvironmentFile=` line from the systemd service an
 - Possibility to change email address for the account
 - Possibility to delete your account
 
+### Changed
+- Signature validation also now checks if `Date` header has acceptable values
+- Actor profiles are now stale after two days and have to be refetched
+- Actor keys are rotated some time after sending a `Delete` activity
+
 ### Fixed
 - Fixed URL search
 - Fixed content accessed through URL search being public