Added automatic access_token refresh when they expire.

[stevenpince]

Problem
The added functionality in #326 (automatic refresh after specific HTTP status code in Zou's response) is wasteful as it puts the responsibility of tracking the access_token's expiration on the Zou server.

Solution
I added a properties to the Client object, that makes access to "access_token" and "refresh_token" easier, as well as the property "access_token_has_expired", that decodes the given JWT access token to determine it's expiration date.

The property is checked in the make_auth_header call, which I have also move to the Client object for a more clear separation of concerns.

If the client's automatic_refresh_token is set to True, the refresh_token (renamed to "refresh_authentication_tokens") method is called to refresh authentication before creating the header - thus theoretically bypassing any possible future NotAuthenticatedError.

This does add the python module "jwt" to the requirements of Gazu - which I haven't added yet to this change.
As far as I can tell, this module should be available from Python 3.6+ - let's check the options

Unittests have been added to showcase the use of these changes and all checks are green.

[stevenpince]

Since checks are turning red due to the missing jwt library, am trying to add the correct one.

[stevenpince]

I added https://pyjwt.readthedocs.io , which I import as jwt - I'm not sure how to declare it properly in the requirements file.

[frankrousseau]

Thank you for your contribution @stevenpince. We are pretty busy at the moment but your code will be merged as soon as we have availability.

@EvanBldy please include this merge in your todo-list.

[EvanBldy]

Hi @stevenpince, good idea thanks!

For pyjwt:
Gazu is compatible with python 2.7 and python>=3.6. So, requirements need the same.
To make it flexible I propose the following:
pyjwt==1.7.1; python_version == '2.7' pyjwt>=2.4.0; python_version >= '3.6'

[steven-pi]

Ok, I am traveling at the moment - will incorporate these changes.

[stevenpince]

Ok, looks like Python 2.7 is breaking because datetime.datetime.timestamp is not available. Let me check if there's a clean way to resolve. Last version of 2.7 is 5.5 years old at this point. What software packages still ship it?

[EvanBldy]

We need to keep Gazu compatible with Python 2.7 for now, some of our clients use some DCC/pipeline that need it.

[stevenpince]

I understand you want to stay Python 2.7 compatible, but datetime.datetime.timestamp was added in 3.3. I tried running a local Python 2.7 environment, but it was just breaking too much for me (requests_mock depends on urllib.parse, which is also not available).

I've gated the functionality for Python3 only. It won't break Python 2.

[frankrousseau]

@EvanBldy Can you review the last changes?

[EvanBldy]

I'm sorry, but I finally don't get the point of parsing the JWT expiration date. It breaks what I made before and knowing from the server if the JWT is expired is not a problem (see here: https://datatracker.ietf.org/doc/html/rfc6749#section-1.5). Also, this is not compatible with Python 2.7 and it will parse the token / check for expiration at each Gazu request.
I prefer that the server tells that the JWT is expired this is just basic and less complex.

Nevertheless I kept some interesting part of the code.