It's Davio, been playing Dominion on and off for, well, more years than I'd like to admit.
Today I saw that Allies was in preview, so I'm super excited to try it out, but I can't find the rules anywhere.
I noticed some cards gave "favors" (as in "+1 favor") which mattered for end game scoring and some cards had the subtype "liaison" which I don't yet know what it does.
If there would be an official link with either card rules or the official rules, that would be great.
So from what I've gathered:
"Favor is a resource which you can gain and/or spend, depending on what specific cards say". It looks like it always comes with a special card, which looks the same as an 'event, project, landmark or way' and always refers to a 'group of people' such as a cult or a league, and is set aside which tells you what favors can be used for in this particular game.
It looks like cards with the subtype 'liaison' can gain favors.