Support new password challenge

[grantmcconnaughey]

This PR adds a method to respond to the new password challenge. It is mostly based off of @stephenoneal's work at https://github.com/stephenoneal/warrant.

Fixes #22

[grantmcconnaughey]

Hmm, not sure why this has the renamed setting commit in there since that has already been merged into develop...

[bjinwright]

It looks good so far. @ebpetway and will still need to integrate it with the warrant.django.views but I don't see anything else glaring at me. @ebpetway thoughts?

[ebpetway]

Tested and seems to work fine.
There's only one possible issue from the perspective of using the Cognito object.

Example:
Say I'm using this in a Django app.
A user inputs their credentials into a login form.
That input is used to instantiate a Cognito object, and then the authenticate() method is used.
If the NEW_PASSWORD_REQUIRED challenge comes up, then this call raises a key error when Cognito tries to pull tokens from the response.

Two ways of handling this could be either to catch the exception, and then call the new_password_challenge method. Or call the admin_get_user boto3 client method and check for a'FORCE_CHANGE_PASSWORD status on the user, so you would know in advance to use the new_password_challenge method.

With that said, I'm ok with getting this initial functionality in.

[grantmcconnaughey]

That's a really good point, and I'm working on this in a Django app so it is something to consider for sure.

What would you think about raising the challenges as exceptions? Like raise a ForceChangePasswordException if that challenge comes up. Then users can catch that exception and handle redirecting the user to a change password page instead.

[bjinwright]

@ebpetway Are you talking about calling admin_get_user before the authenticate?

[grantmcconnaughey]

Okay, I've changed the flow a bit and I think it's better now. Now users will handle the flow like this:

cog = Cognito()
try:
    cog.authenticate('oldpassword')
except ForceChangePasswordException:
    cog.new_password_challenge('oldpassword', 'newpassword')

Also, @bjinwright, if I need to do something to cleanup the commits on this PR then I can. Not sure why it says the PR has so many commits. 😕

[bjinwright]

That's because we had some merge conflicts that I cleaned up yesterday

[bjinwright]

@grantmcconnaughey @ebpetway Here is the workflow I think we should go with.

1. User attempts to log in
2. The view from the framework calls admin_get_user before attempting to authenticate and based on the users status we either call authenticate because the user's status is CONFIRMED or return a redirect response based on the user's status.

What's Needed to Make it Work

1. Different methods for each scenario
2. Different views for each user status scenario (UNCONFIRMED | CONFIRMED | ARCHIVED | COMPROMISED | UNKNOWN | RESET_REQUIRED | FORCE_CHANGE_PASSWORD)

[grantmcconnaughey]

Makes sense to me! The only downside I can think of there is that most of the time unnecessary calls to admin_get_user will occur because (in theory) most of the time they are confirmed users attempting to login.

With the exception-based approach most of the time the authenticate method is the only thing that will be called. The Challenges would be raised with what they are -- exceptions to the normal flow.

[bjinwright]

I decided to merge this as is

[grantmcconnaughey]

Cool, thanks Brian!