add duo authentication support

[si458]

Fixes #2432

"passwordRequirements": {
  "duo2factor": {
    "apihostname": "api-xxxxxxxxxx.duosecurity.com",
    "integrationkey": "xxxxxxxxxxxxxxxxxx",
    "secretkey": "xxxxxxxxxxxxxxxxxxx"
  }
},

[Ylianst]

This is amazing. Working on checking security and will release. I will be using this myself.

[Ylianst]

I am making a few fixes to this one before general use. The Duo setup will need some improvements before release. I am traveling for 4 days, but once back, I will take care of it.