אורח חיים קי״בOrach Chayim 112

Se’if 1א׳

אַל יִשְׁאַל אָדָם צְרָכָיו בְּג' רִאשׁוֹנוֹת, וְלֹא בְּג' אַחֲרוֹנוֹת; וְדַוְקָא צָרְכֵי יָחִיד, אֲבָל צָרְכֵי צִבּוּר שָׁרֵי.

That One Should Not Interrupt [the Amidah], Neither In The First Three [Blessings] Nor in the Final Three. Containing 2 Se'ifim: One should not ask for one's needs in the first three [blessings of the Amidah] nor in the final three. And this is specifically [regarding] the needs of the individual, but [for the] needs of the community, it is permitted.

Se’if 2ב׳

אֵין לוֹמַר פִּיּוּטִים וְלֹא קְרוֹבֵץ (פי' קְרוֹבֵץ לְיוֹצֵר, וְיֵשׁ אוֹמְרִים שֶׁהוּא רָאשֵׁי תֵּבוֹת קוֹל רִנָּה וִישׁוּעָה בְּאָהֳלֵי צַדִּיקִים) בַּתְּפִלָּה. הַגָּה: וְיֵשׁ מַתִּירִין, הוֹאִיל וְצָרְכֵי רַבִּים הֵם (הָרֹא"שׁ וְהַתוס' וְהָר"י וְהָרַ"ן רֵישׁ פ' בַּתְרָא דְּרֹאשׁ הַשָּׁנָה וְהַגָּהוֹת מַיְמוֹנִי פֶּרֶק י' וְטוּר), וְכֵן נוֹהֲגִים בְּכָל מָקוֹם לְאָמְרָם.

One should not say liturgical poems nor a "krovetz" (meaning "krovot l'Yotzeir" [close to the blessing of Yotzeir Or], and some say it is an acronym for "Kol Rina Vi-shua B'ohalei Tzadikim" [Psalms 118:15]) during the prayer [i.e. Amidah]. Gloss: And there are those who permit [them], since they are [considered] needs of the public (the Rosh; Tosefot; the Ri; and the Ran at the beginning of the last chapter of Tractate Rosh Hashana; and Hagahot Maimoni, chapter 10; and the Tur), and such it is practiced in all places to say them.