[1.6.x] Fixed a French translation in contrib.auth

Refs #22929.
[1.6.x] Fixed docs/ref/contrib/auth.txt so that sphinx links work properly.

Backport of 5359188b08 from master
[1.6.x] Removed reference to old middleware

Backport of 0b5bafe993 from master
[1.6.x] Fixed #19489 -- Documented host parameter of assertRedirects().

Thanks mrknacky at gmail.com for the report and gajimenezmaggiora
for the draft patch.

Backport of e3c7af18a3 from master