Is it possible for the Vedas to have been authored?
Yes, they were authored. First off, here is some background information: If a text is authored, then it can be doubted because the author might be wrong. Thus we can doubt the Bible, Koran, etc. and all other spiritual and scientific texts because the writers could be wrong. But if a text is authorless, then there is no basis to doubt its validity, and hence it must be accepted:
Shabara bhashya on Purva Mimamsa sutra 2:
[human authorship can be doubted], but in the case of the Vedic assertion on the other hand, there is nothing to indicate its falsity.
Thus, if one can show a text is authorless, then one establishes the validity of that text. It is for this reason that ancient Hindu scholars advanced a massive propaganda campaign to show that the Vedas are unauthored when there is tons of evidence to the contrary. How did they do this? By showing that all declamatory and historic statements in the Vedas are false, that the gods do not exist, Brahman does not exist, and all smritis are false. By doing so, all the mantras in the Vedas that speak of authorship of the Vedas by the Rishis would be rendered false.
For example, here is the Purva Mimamsa argument in the Sri Bhashya of Ramanujacharya:
For if Indra and the other gods are corporeal beings, it follows that ...[they are] non-permanent. This implies ...that ...the Veda itself is non-permanent, non-eternal.
So, this argument was fabricated by Jaimini and the proponents of the Purva Mimamsa school at the beginning of the kali yuga to get believe to believe in the Vedas at all costs, because in kali yuga, people do not see the Devas, supernatural beings, or have experiences of Brahman to create mantras.
But as a matter of fact, before the kali yuga, people believed that the Vedas were authored by the Rishis. For example, the extremely ancient Yaska, author of the Nirukta, says in the Nirukta:
1.20 - The rishis were the ones who had a direct vision Dharma. For the sake of the inferior people who were not endowed with a vision of Dharma, [the rishis] gave mantras as instruction/teaching. This is the Veda and Vedāṅgas.
7.3 - Thus, the visions of the rishis occur with various intentions and topics.
Yaska lived in a previous yuga.
And mantras in the Vedas like the following all show that the Vedas were authored:
RV 1.61.4: asmā idu stomaṃ saṃ hinomi rathaṃ na taṣṭeva — “For
him, I design this hymn, just as a carpenter designs a chariot”
RV 1.94.1: imaṃ stomamarhate jātavedase rathamiva saṃ mahemā manīṣayā
— “This stotra we make for the most sacred Jātaveda with deep
meditation, just like building a chariot”
Sri Bhashya (uncited Veda) - 'He [Brahman] chooses the makers of
mantras'; 'Reverence to the Rishis who are the makers of mantras';
'That is Agni; this is a hymn of Visvâmitra.'
If the mantras were just "eternally passed down orally" and were "never created", then there would be no mention of "building them like chariots". The Purva Mimamsa school would say that these mantras have no ability to convey facts (they are meaningless).
Moreover, the Vedas have conversations between people, mention historic events like battles, talk about the Rishis life experiences, their sexual experiences and fantasies, mention temporal and relative things, and only take place in the limited area of North India, which is where the Rishis lived. If the Vedas are eternal and authorless, then they would describe other geographic locations where the Rishis didn't live.
For example, there are mantras like, "a new language is being developed in the northern countries". This is obviously a temporal and relative statement composed during a time when this was true.
Thus, the Vedas are authored by the Rishis. But this doesn't mean that the Vedas are not credible. They are credible because they are authored by trustworthy Rishis based on their spiritual experiences of direct apprehension of Brahman. The Vedas consist of stories of spiritual experiences of the Rishis. This is a common theme in the Vedas. For example, in the Bhrigu Valli of the Taittiriya Upanishad,
He perceived that food is Brahman, for from food these beings are
produced; by food, when born, they live; and into food they enter at
their death. Having perceived this, he went again to his father
Varuna, saying: 'Sir, teach me Brahman.'
And in the Brihadaranyaka Upanishad:
The Rishi Vâmadeva saw and understood it, singing, 'I was Manu (moon), I was the sun.'
And this has been declared by a Rishi (Rv. IV, 27, 1): 'While dwelling in the womb, I discovered all the births of these Devas. A hundred iron strongholds kept me, but I escaped quickly down like a falcon.' Vâmadeva, lying in the womb, has thus declared this. And having this knowledge he stepped forth, after this dissolution of the body, and having obtained all his desires in that heavenly world, became immortal, yea, he became immortal.
But ultimately, it is Brahman who authors the Vedas through the medium of the Rishis, as this mantra says:
'He [Brahman] chooses the makers of mantras'.