The person I was responding to said these providers “should never get hacked”. Given that the default assumption is that systems are easily hacked, then logically such a requirement demands proof (in the sense of robust evidence) before acceptance that it is met. There is no sense in waiting for it to happen first when that is the default assumption.
To go a step further, you can apply this to any acceptance criteria. What evidence is there that any of these systems meet any meaningful acceptance criteria. What evidence is there that Okta has systems that can protect billions of dollars worth of assets from the teams of professional and state attackers that currently target their systems?
To then get to your direct question, if you really need “should never get hacked”, you could provide machine checked mathematical proofs of correctness, robust and exhaustive validations, and NSA penetration test reports showing zero identified vulnerabilities like what was done for the F-35. I mean, I guess that is only like 1000x better than prevailing commercial IT systems and not completely foolproof, but it is certainly a good starting point. You can probably think of some ways to evaluate even more robust security if you need more assurance than the US air force.