digraph twofa {
  bgcolor=transparent;

  "Start" -> "Login + password"
  "Login + password" -> "Password correct?"
  "Password correct?" [shape="diamond"]
  "Password correct?" -> "Wait" [label="no" color="red" fontcolor="red"]
  "Wait" -> "Login + password"
  "Password correct?" -> "2FA Cookie < 90 days\nfor 'Login'?" [label="yes" color="green" fontcolor="green"]
  "2FA Cookie < 90 days\nfor 'Login'?" [shape="diamond"]
  "2FA Cookie < 90 days\nfor 'Login'?" -> "Success" [label="yes" color="green" fontcolor="green"]
  "Success" [color="green" fontcolor="green"]
  "2FA Cookie < 90 days\nfor 'Login'?" -> "Send OTP challenge" [label="no" color="red" fontcolor="red"]
  "Send OTP challenge" -> "OTP success?"
  "OTP success?" [shape="diamond"]
  "OTP success?" -> "Put dated 2FA cookie" [label="yes" color="green" fontcolor="green"]
  "OTP success?" -> "Too many failed\nattempts?" [label="no" color="red" fontcolor="red"]
  "Too many failed\nattempts?" [shape="diamond"]
  "Too many failed\nattempts?" -> "Send OTP challenge" [label="no" color="green" fontcolor="green"]
  "Too many failed\nattempts?" -> "Blocked account" [label="yes" color="red" fontcolor="red"]
  "Blocked account" [color="red" fontcolor="red"]
  "Put dated 2FA cookie" -> "Success"
}