Password policies: option to disallow consecutive repeated characters

Is your feature request related to a problem? Please describe. Password policies can constrain length and require a minimum number of characters from given charsets, but they cannot prevent the same character from appearing twice in a row. Some downstream systems and organizational password standards reject passwords with repeated adjacent characters (for example, aa or 11). Today there is no way to express that constraint in a Vault password policy, so passwords generated by Vault can be rejected by the target system, and the failure only shows up at credential rotation time.

Describe the solution you'd like A new optional top-level attribute in the password policy HCL:

length = 20
consecutive-chars-allowed = false

rule "charset" {
  charset = "abcdefghijklmnopqrstuvwxyz"
  min-chars = 1
}