Investigate adding 2FA to NiFi

It would be great to see two-factor authentication options added to NiFi. I believe there can be two solutions which can be investigated and added:

1. External identity providers which offer 2FA/2SV (easy)
   1. Allow a NiFi administrator to enforce 2SV for NiFi users
2. A native solution (hard)
   1. Will require some level of native user tracking to track shared keys per user for TOTP. Currently NiFi stores basically no details of users or their passwords.
      1. Secure hashing of passwords using bcrypt/scrypt or some other password hashing mechanism
   2. Uses an open source library to handle TOTP
      1. Must allow users to initialize, enter and verify TOTP values