v208.go is seriously broken as it misses an ID() check. We need to no-op and remigrate all of the u2f keys.
See #18756
Signed-off-by: Andrew Thornton <art27@cantab.net>
- Switch to use `CryptoRandomBytes` instead of `CryptoRandomString`, OAuth's secrets are copied pasted and don't need to avoid dubious characters etc.
- `CryptoRandomBytes` gives  `CryptoRandomString` gives  possible states.
- Add a prefix, such that code scanners can easily grep these in source code.
- 32 Bytes + prefix