I mostly use flask. I have not come across a complete SAAS boilerplate in flask ...

I mostly use flask. I have not come across a complete SAAS boilerplate in flask but you can probbaly put one together by using some of these great flask extensions:

    Flask-Security [0] . Takes care of the following:
      
        Session based authentication
        Role management
        Password encryption
        Basic HTTP authentication
        Token based authentication
        Token based account activation (optional)
        Token based password recovery / resetting (optional)
        User registration (optional)
        Login tracking (optional)
        JSON/Ajax Support

    Many of these features are made possible by integrating various Flask extensions and libraries. They include:

        Flask-Login
        Flask-Mail
        Flask-Principal
        Flask-Script
        Flask-WTF
        itsdangerous
        passlib

    Additionally, it assumes you’ll be using a common library for your database connections and model definitions. Flask-Security supports the following Flask extensions out of the box for data persistence:

        Flask-SQLAlchemy
        Flask-MongoEngine
        Flask-Peewee

    Using stripe with Flask [1]: Follow this guide on stripe's docs.

[0] http://pythonhosted.org/Flask-Security/

[1] https://stripe.com/docs/checkout/guides/flask