Allow render_template to be overwritten

[rochacbruno]

HI,

I am using a Flask-Themes application https://github.com/pythonhub/quokka-themes

I can customize the theme for almost all apps, even for Flask-Admin I can do it by extending the main class

from flask.ext.admin import Admin

class MyCustomAdmin(Admin):
    def render_template(self, *args, **kwargs):
        # here I load my theme template

But I was trying to do the same with Security

from flask.ext.security import Security

class MyCustomSecurity(Security):
    def render_template(self, *args, **kwargs):
        # here I load my theme template

But I figured out that Security main class does not expose a render method to be ovewritten.

It is now being done directly by the views, so I suggest to have a method and use this for rendering templates, or maybe have a config variable.

SECURITY_RENDER = 'somewhere.module:render_template'

So with the above setting you can do in views.py

from werkzeug.utils import import_string
render_template = import_string(config.get('SECURITY_RENDER'))

Having its default to a normal render_template from Flask.

But I prefer the first case when the class expose a render method to be overwritten.

By now I will create a fork and implement that for my specific case.. If I got some idea I will send a PR.

What do you thing about it? @mattupstate