Commit password change

[Digant Kasundra]

Can someone tell me where in the code a password change is actually
committed?  I see a handful or wrappers and related functions but I'm
curious is there is one single point where a principal/password pair are
written.
 
My plan is to hook into that function to send principal/password pairs to an
external auth service so that passwords can stay in sync.
 
Any help or clues would be appreciated!
 
 
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Digant C Kasundra