In Laws of Repentance 2:6,7, Rambam
How do we reconcile our testimonials in groups, on boards, or to a partner/sponsor/friend with confession of sins between man and G-d being brazenness?

I think there's a difference between being Mefarsem in public, and sharing privately with an individual who can help you. See The Tzetel Kotton of R' Elimelech Lizensker:

However, another part of this step is admitting one’s sins to a human being. This specific component of the 5th step is questioned by people because it seems to contradict a Gemara in meseches brachos 34b which says that telling a human being one’s sins is forbidden; if the Gemara says it is forbidden to talk about one’s sins with other people, then how can it possibly be permissible to do the 5th step?
This may be the only legitimate question on the 12 steps, although you will soon see that it also has a legitimate answer. In fact, you already rely on the answer that I will give in other ways in your life, even if you are not a member of AA.
In the original edition of this paper I wrote a lengthy teshuva on this step. In this edition I have shortened it to the bare bones of why it is permitted in halacha to do step five and admit one’s sins to a sponsor.
The answer simply is, the Torah forbids sharing one’s sins when it has no constructive purpose. However, if the sins are being told over for the purpose of seeking guidance or in the context of working a spiritual program to sober up from addiction, this is permitted. Not only that, it seems to be the minhag Yisrael as well. If this idea was not true, it would not be permitted to discuss one’s spiritual problems with a Rabbi, Mashgiach, or Chasidic Rebbe in order to seek guidance.
Rabbi Twerski is known to bring the source for this from Reb Elimelech of Lizhensk in his Tzetel Katan. Although I was originally bothered that Reb Elimelech seemed to be the only one who writes that this is permitted, I later understood that no one else wrote this is permitted simply because it is so obvious that it is unnecessary to speak out. Indeed, all the Rabbanim that reviewed this paper said this idea is obvious, and that it is clearly the custom of Klal Yisrael to understand the halacha in this way.
The letter of Rabbi Twerski on this topic can be found in sefer Yishmaru Da’as, vol. 2, p. 116; The Tzetel Katan itself is in the Tzetel Katan paragraph 13.
(Author’s note: The Shlah Hakadosh (Sha’ar HaOseeyos, Chess, Chaver Tov 2 quoting Rabbeinu Yona in Igeress Hatshuva 97) brings from Rabbeinu Yona a general statement about the importance of having a friend in regards to doing teshuva, so that if one friend veered off the path of teshuva, he can share this and then the person he shared the information with can rebuke him and influence him to return to the path of teshuva.

The language that the Shlah quotes from Rabbeinu Yona may only support that idea of sharing general information with one’s friend, but not sharing specific sins. However, in the Yad Rama edition of the Shlah Hakadosh, they note (see footnote 89) that the text quoted by the Shlah of Rabbeinu Yona is different from the actual text that we have today.Take a look at the version that we have in our edition of Rabbeinu Yona, which says:
“The way a man should conduct himself in order to achieve fear of heaven is to find one or two good friends to be able to speak to them constantly in topics concerning yiras shamayim. If one of the friends sins or fails to perform one of the positive mitzvos, his friend can rebuke him, and they can rebuke one another on each sin that the other one did”.
According to this text of Rabeinu Yona, it seems that it is permitted for friend “a” to share his specific sins with friend “b” so that friend “b” can rebuke the sinner, friend “a”, specifically for that sin. Rabeinu Yona seems to imply that it is permitted to share one’s specific sins with a trusted friend for the constructive purpose of doing teshuva; if friend “a” didn’t share his specific sin with friend “b” then how would “b” ever know about it in order to rebuke “a”?
It is still possible to say that one cannot draw any proof from here either because of an alternative way of reading this text, which suggests that speaking with the friend in yiras shamayim is one idea while being rebuked is another. According to this reading, friend “b” is not rebuking “a” because “a” told anything to “b”. Rather, it may simply have happened that “b” saw with his own eyes something that “a” did, and he rebuked him for this.
Nonetheless I think the original, more simple way to read the text of Rabbeinu Yona is also a possibility-according to this reading of the text, Rabeinu Yona is telling us that the two friends should talk in yiras shamayim constantly, which means to always check in with one another about sins and mitzvos, so that if one is slacking off, the other friend can rebuke him, vidok, vian kan makom liha’arich, eyin sham.) Similarly, it is possible to understand the Tzetel Katan in an alternative fashion-that Reb Elimelech is referring specifically to urges and bad thoughts that come to him naturally, but he is not referring to actual sins and thoughts that the man conjured or devised on his own-therefore, there is no absolute proof to say from here that according to Reb Elimelech, one can share his sins with a trusted friend for a constructive purpose, because in the actual text of the Tzetel Katan, the man there may have not done any sin at all-since the halacha is that it is not a sin to have sexual or evil thoughts-it is only a sin to prolong or create such thoughts. Vidok gam bazeh, yaish liayin vian kan makom liha’arich.)
The point is that all said and done, all the poskim and talmidei chachamim that I consulted with, as well as the basic understanding of the reason behind the Gemara in Brachos 33b, as well as the support from Sota 7b, as well as the custom of klal yisrael-all of this together permits step five beyond the shadow of any doubt. <-See Igros Moshe Orach Chaim 4, 118 who also permits this, eyin sham. Below I will quote him.

Now I will briefly expand on additional sources for this Halacha. In the very source in the Gemara where it teaches the law restricting people to share their sins with others, it provides a reason for this law-that by sharing our sins with other people, it appears as if the person telling the story is not embarrassed about what he did (source for this interpretation-Rashi, Sota 7b & Yoma 86b, also Tosfos Brachos 34b) and this is a desecration of Hashem’s honor. Consider the fact that the Gemara in Sota 7b teaches that relating one’s sins to another is permitted when there is a constructive purpose-the case of the Gemara there is relating one’s sins to somebody in order to remove suspicious from other people, eyin sham.
It comes out from these two places that although it is forbidden on the one hand to share one’s sins since it appears that he is careless about his sins, it is still nonetheless permitted to do so when there is a constructive purpose.
This helps us understand better the source in the Shulchan Aruch that forbids saying over one’s sins in public. The Shulchan Aruch there has a case where a man is praying on Yom Kippur in shul, alongside everybody else. The Shulchan Aruch says that it is forbidden for this man to specify within the general confession of Yom Kippur all of his personal sins of that year, in a way that the other shul members can hear what his sins were. This is because of the original Gemara we quoted that says it is a desecration to God’s name to tell other people one’s sins.
This is forbidden because the man specifying his sins has no reason to do so out loud; because of this simple fact, it is forbidden. However, if there was a compelling reason why this had to be done, it would be permitted. A case where saying over one’s sins to another is necessary is the case of an addicted Jew who joined a 12 step group and needs to do step 5 in order to recover from addiction. In this case, the intention is noble and it is certainly no less of a constructive purpose than the reason why sharing one’s sins is permitted in the Gemara of Sota 7b. I reviewed this with 4 Rabbis and Poskei Halacha in Yerushalayim, where I live. They unanimously agreed that this halacha formulation is correct and obvious (see also the Mayim Chaim brought by Mekoros ViTziyunim in the Frankel edition of the Rambam, hilchos Teshuva 2, 5) who writes that revealing one’s sins for a constructive purpose is permitted; see also Sheilos U’T’shuvos Noda BiYehuda Even Haeizer, 72 who writes “One time before Rosh Hashana…several people came before the Beis Din and

specified the aveiros that they did that year in order to confess their sins and to ask the Beis Din for guidance on how to do teshuva…”. Eyin sham, upashut, vian kan makom liha’arich.
Even when permitting step 5 in halacha, some Jewish AA critics make a fuss and claim “well, it has a Catholic taste to it so it is no good anyways, even though permitted by halacha!”
I know one Rabbi who replies to this with what he calls “the Judaism of the Shulchan Aruch”, which means that we Orthodox Jews know whether something is Jewish or not by whether it is permitted or not by the halacha. If the Jewish people were to decide what is Jewish or not based on emotion, we’d end up no longer observant. It is halacha that guides the Jewish people towards the correct conduct; it is halacha that reveals to us God’s will in this world, despite the fact that we have no prophets anymore.
I personally like to reply to this with the Rambam (source-see Rambam in hilchos Teshuva 2, 5. Here, the Rambam writes “It is worthy of great praise regarding a Ba’al Teshuva when he confesses his sins in public that were done to his fellow man and to specify ‘I did this and this to Mr. so-and-so’…and anyone haughty that doesn’t confess these types of sins in public, his teshuva is not considered complete, because the pasuk says “the one who covers up his sins will not be successful”.
Even though the final practical halacha set out in Shulchan Aruch (Yom Kippur 607,2) holds that one should not share his sins to others, you see from the Rambam that confessing certain types of sins in certain settings is a Jewish idea. According to the above Rambam not only was this considered an acceptableJewish practice, but he writes that without doing this step of teshuva, one’s teshuva is not complete!
Despite that the Rama in Shulchan Aruch decided for us to act otherwise in halacha, we cannot say about the view of the Rambam that it is a Christian practice because at the end of the day, one of the greatest rishonim in history held that this was the halacha, making it within the realm of “eilu vi’eilu diverei Elokim chaim” (these as well as these are the words of the living God); this is no different than Beis Shamai, who we do not follow as final halacha in most cases, but we do not regard his opinion as being Christian just because we follow Bais Hillel instead.

While finishing the writing of this paper, I came across a response from R’ Moshe Feinstein on our very topic (see Igros Moshe Orach Chaim 4, 118; quoted by sefer Mishpatei Hashalom p. 221 in footnote 34). There, R’ Moshe writes to a girl who was promiscuous and now wants to repent:
“You also need to know that when you repent, it should be silently so that other people do not hear what you did…...only when there is a constructive purpose is it okay to reveal your sin to somebody else so that they can tell you how to repent in Halacha or so that they can give you good advice about how to stay out of repeating the sin, and that’s why it was good that you wrote this letter to me since you wanted to know what to do to avoid sinning again in the future…but if there is no constructive purpose to revealing one’s sin, then it is forbidden, because only lowly people in other cultures do this since they believe that by telling their sins over to a religious figure, this alone will consider the sin “undone” and forgiven, and then it is as if the person is allowed to go back to sin again and again [as long as he keeps coming at intervals to get “forgiven” by the religious figure]. The way of our Torah is the opposite, to hide one’s sin unless there is a purpose to know how to repent or how to overcome the evil inclination in that area”.
We see clearly from this responsa of R’ Moshe that:
a) Telling over a sin for a constructive purpose to know how to repent or how to overcome the evil inclination in this area is permitted
b) It is forbidden to share a sin with a person that, so-to-speak “undoes” and forgives the sin, encouraging and enabling the sinner to sin again and again and just come back for his regular “cleansing”.
Of course, Jews in 12 step programs do not share their sins with their sponsor in step five in order to be “cleansed” by them! They do this so that they can overcome their evil inclination and interrupt the harm they are doing to themselves and others as a result of their addiction.
Just remember one thing from all of this-that step five is fine in Halacha.

Wow, thanks for your very thoughtful teshuva (pun intended)!

I – bli neder – think I'll take look at the sugya on shabbos. It seems pretty interesting. So the relevant gemaras are Brachos 34b, Sota 7b and Yoma 68b? Do you know what the R Yonah is going on? S"A Yom Kippur 607,2, and do you know the se'ifin for the other halachos in S"A? And then the Rambam, of course, and the achronim, which I certainly won't get to in one shabbos, and seem to be documented pretty thoroughly in your article.