In the show (and I presume in the books as well) they make a pretty big deal about the physical bodies being merely "sleeves" to be discarded and replaced. However, everything from payments to secure locks seem to be DNA based, which doesn't make sense. The problem is even outlined in the show when Kovacs realizes that Bancroft's kids secretly use theis parents's clones, giving them acces to the DNA-locked weapon cabinet. Shouldn't authentication be tied to their stacks in stead? Is there an in-world (or not) explanation for this?
While not explained in detail in either the book or series, there is some sense behind it:
Interfacing directly with the stack is somewhat invasive and not really suitable for frequent transactions, like paying for your daily meal. A wireless connection to your stack occurring every time you make a purchase is similarly a huge security risk.
Most people do not change stacks, and certainly not often. When they do, it's almost always under circumstances that have some level of oversight, like an accredited hospital, or resleeving clinic, and as such one can imagine procedures in place that let the bank know "okay, this stack is now connected to this body, update the DNA record required to access the account." People who regularly change stacks would obviously have considered the problem and any additional precautions they needed to take.
Stacks also carry their own problems. Although it doesn't get much into it in the series, in the book it's described as pretty difficult to get any specific information artificially from a stack - this is why the torture clinic was necessary, otherwise why not just read their mind. So, what do you scan to verify their identity? You can't use a serial number on the stack itself, because stacks are generally interchangeable, it's the data inside them that's important. Maybe you could scan for an overall 'signature' that identifies the particular stored consciousness (but what happens if they go through significant life changing experiences that change who they are?). In the end, it's all just data, which can be manipulated. When you think about it, the best scan for identity that relies on a stack is the person knowing a particular password and sending it from whichever body they're in, which is probably also done, depending on the circumstance and their individual propensity for stack-switching.
You can imagine it similar to the chip payments on cards that let you just tap your card on a sensor to pay quickly, rather than inputting your PIN - it's theoretically incredibly insecure because anyone who gets their hands on your card can then do it, but for the most part, people prefer the convenience, and you can set it so that transactions under a certain amount are processed automatically, but for more expensive things you need more robust identity confirmation (that may come from stack probing, passwords, etc). People like Laurens Bancroft, who have such huge amounts of money that they're barely notice if someone stole what would be a life-changing amount for someone else, will have comparatively higher thresholds. And he may have assumed that he was at no risk from stolen clones, because who would dare?
Unlike a password, you never have to worry about forgetting your DNA or giving the wrong one. Unlike a card, you never lose your DNA (except in the case of a new sleeve which is, again, rare and usually happens in circumstances where updating your access credentials is easy)... and, although your DNA can be copied pretty easily, sensors might be able to detect how fresh the sample is, etc, and make that more complicated than it is in our world, not to mention that it would be a crime, and that a purchase might trigger an alert to the actual owner of the account who can instantly alert authorities.
It's obviously not a perfect system, and probably not used universally, but it's good enough for everyday life.