Full disclosure here, I'm not Orthodox, I'm a Reform girl, but this is what I was able to grab, insomuch as understanding where the Orthodox position stands on rabbinic authority.
First, some clarification. Halacha is Jewish law with a practical basis. Aggadah, which was not passed down from Halacha L'Moshe Mi'Sinai, is Jewish folklore. Today, we won't be ...
It depends which kind of rabbinic authority you are talking about - nowadays there isn't much. When there was a clear centralised rabbinic body accepted by all, that had a power similar to that of the Sanhedrin. See How does halacha work?
Their job of determining the true understanding of texts
I have heard from many sources, Rabbi Orlofsky being the most recent. The idea that the fact that the torah says
וְאַתָּה דַּבֵּר אֶל בְּנֵי יִשְׂרָאֵל לֵאמֹר אַךְ אֶת שַׁבְּתֹתַי תִּשְׁמֹרוּ כִּי אוֹת הִוא בֵּינִי וּבֵינֵיכֶם לְדֹרֹתֵיכֶם לָדַעַת כִּי אֲנִי ה' מְקַדִּשְׁכֶם: וּשְׁמַרְתֶּם אֶת ...
I don't think that you will be able to find a solid source, because during the biblical era the authority came from the prophets, not Rabbis. After prophecy stopped, the Rabbis took over the prophets.
בבא בתרא יב א
אמר אמימר וחכם עדיף מנביא
Bava Batra 12a
Amimar said, a sage is better then a prophet.