Kabala in Halacha

Which of the major authors or codifiers of halacha. . .

a) refer directly to or quote from kabala in their legal discussions?

b) employ conclusions based only on kabala in their legal argumentation and decisions?

Answer

First as far as being posek al pi Kabbalah the inyan is only L'Humra not L'kula. For instance the Zohar says one needs only to wait a half hour between eating meat and eating milk, but we do not hold that way.

Aside from that the list becomes quite extensive as Chanoch also said, from the Ramban down to today amongst Sephardi poskim. Of the modern Sephardi poskim, there is Rav Mordekhai Eliyahu ZTz"L, Rav Ovadiah Hedayya ZTz"L, Rav Ezra Attiah ZTz"L, Rav Yehuda Tzedaka ZTz"L, Rav Ben Tzion Abba Shaul ZTz"L, Rav Ovadiah Yosef ZTz"L, Rav Shlomo Amar Shlita ect. ect...

Then there were the Misnagdim, such as the Magen Avraham, GR"A and R' Haim of Volozhen.

Then there are the Hasidic Admurim.

Essentially poskim who consider what is written in Kabbalistic sefarim can be found in nearly every stream of Orthodox Judaism.

As far as employing conclusions based solely on Kabblah, not even the Ar"i HaKodesh did that. A good example is the time of laying Tefillin, al pi Kabbalah any time after Hatzot HaLailah is suitable. However the AR"I in defference to the Gemarra and prior poskim, restricted the time to no earlier than Alot HaShahar. There are excellent work ups on the entire Teshuva in R' Ovadiah Yosef's Halichot Olam, and R' Apjin's sefer Divrei Shalom, unfortunately neither are online. Ultimately the essential point is that the Kabbalah, is the inner aspect of the Torah, as such, and as many Mekubalim have elucidated to the point where to list them all would be an exercise in futility, though it is expoused briefly in the introduction to Eitz Haim, and the introduction of Sha'ar HaKavvanot, the Kabbalah gives a deeper meaning to the mitvot, and halakha, but can never directly contradict the p'shat(aka Halakha).