Notable changes:
- Support of $2b$ password format to address a problem where very
long passwords (more than 256 characters, when an integer
overflow would happen and cause the length to wrap at 256).
- Updated pseudo code in comments to reflect the reality.
- Removed our local shortcut of processing magic string and rely
on the centralized and tigntened validation.
- Diff reduction from upstream.
For now we are still generating the older $02a$ format of password
but we will migrate to the new format once the format is formally
finalized.
MFC after: 1 month
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