If you create a TreasuryDirect account using my SSN, do you then require a durable power of attorney to manage it on my behalf, as laid out in 31 CFR § 363.33? Or are you simply logging in using "my" credentials and performing actions as if you were me? If the latter, are you at all worried about the Treasury Department cracking down on this?
https://www.law.cornell.edu/cfr/text/31/part-363/subpart-B
From a brief reading, having a third party access your TreasuryDirect account does seem problematic:
I liked the description of the product when I first read it. I really did. But I'm losing confidence the more OP keeps pushing in the comments.
This might be a decent product, but I'm wary of someone who is pushing hard to let them create investment accounts on other platforms on our behalf. It just feels like the kind of thing that when it blows up in the future, hindsight will say, "Why did you let someone do that in the first place?"
YOLO is definitely an interesting approach for a financial company. Didn't people shit all over Plaid for taking this approach? Training people to give their financial credentials to 3rd parties is not the best.
Keep it up! You're acting for the good of the user, YOLO it.