'True' here is most definitely an adjective, since the phrase is elliptical for
'accepted as BEING true'.
Regarding the status of 'as', however, not all linguists would agree.
Traditionally, 'as' is classified as a conjunction, but, as such there would, strictly speaking, have to be an implicit finite verb, which, in this case, is - to say the least - difficult to identify. For that reason (as in such constructions as 'I say this as your father', with 'as' meaning essentially 'in the role/capacity of') many grammarians would consider it to be functioning here as a preposition.