Do you have to prove your disability to a TSO when asked? No.

Does a TSO have to allow you to proceed through the checkpoint? No.

Irresistible force, meet immovable object.

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Seriously, though ... common passengers aren't allowed to know what the rules are at a TSA checkpoint. The rules are whatever the screener in front of you says they are. I suspect that, the vast majority of the time, this sort of event doesn't happen. But it happens often enough to become commonly reported in forums such as these.