Password and user management from external application

I'm working on a project with 50+ Sitefinity 3.6 & 3.7 websites.  We'd like to build a central user management application to mass email and reset passwords etc.  We'll also evenutally be adding a new user insert option too but not in the first phase.

The Sitefinity sites all have passwords set to hashed.  Where is the hash algorithm (or which one do I need to use) so that I can reset new user passwords from a 3rd party application?

Thank you for your help.