2FA manual entry uses wrong encoding

Summary

As in report #260491, a security researcher discovered that following another change (from report #259415), we used the wrong encoding for the manually entered secret. No sensitive data was exposed and there was no security risk, but users were unable to manually register a new TOTP device for about 12 hours.

@vishnuprasad reported this issue first, but due to a clerical error, report #260491 was processed first, awarded a bounty, and closed as Resolved. It is therefore only fair to award the same bounty to @vishnuprasad and close this report as Resolved. @vishnuprasad, we apologize for the error and have awarded a bonus for our mistake.