The first sentence with "s'est passé" is not semantically correct as the interlocutor has not yet had the interview (but it is grammatically correct).
The passé composé should only be used when the action is in the past when we talk (for instance see here).
Vous me raconterez comment s’est passé votre entretien à votre retour.
we should understand that the interview is already in the past (when the interlocutor is talking).
But (as said in the comments) this tense is more simple and is often used as, in many situations, there is no ambiguity about the "when" the action was or will be accomplished.
The difference is more obvious in this example (and probably in many cases using a verb with "avoir" as auxiliary):
Tu me diras quand tu as terminé (incorrect)
Tu me diras quand tu auras terminé (correct)
PS about the (un)certainty mentioned in the comments: these tenses are not used to express a doubt or uncertainty even if what we are talking about may never occur. The sentence itself is not uncertain: "when X, then Y" can be always true even if X never occurs.