Terminate all UAA sessions at the server level

[rogeruiz]

This addresses #810 with the following solution.

If the user is authenticated
  Clear Django user session
  Redirect to UAA server with Client ID and Redirect parameters
  Redirect to application logout page
If the user isn't authenticated
  Show the application logout page

[rogeruiz]

In order to deploy this to production, we need to add the https://tock.18f.gov/logout URL to the redirects array in the client.

[ccostino]

Woohoo, thank you so much for tracking this down and following up on it, @rogeruiz!

[ccostino]

Wouldn't it be better to leave this as user.username, or are you going for the repr/str defined on the model instead by doing this?

[rogeruiz]

The value that got sent over after the redirect was no longer a Django user but rather the string of the user. This was occurring after the redirect I believe. when I user user.username it was hitting an error. I figured it's also easier to just rely on the str defined on the model anyway here. It never felt right to drill down into when the string representation of the User model could change and be more useful.

[rogeruiz]

Whoops, gotta fix the tests here! 🐠

[codecov-io]

Codecov Report

Merging #814 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #814      +/-   ##
==========================================
- Coverage   90.85%   90.82%   -0.03%     
==========================================
  Files          38       38              
  Lines        1716     1722       +6     
==========================================
+ Hits         1559     1564       +5     
- Misses        157      158       +1

Impacted Files	Coverage Δ
tock/views.py	71.87% <0%> (+2.64%)	⬆️

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[ccostino]

Looks good now, thanks @rogeruiz! Let's verify once more in staging too, once it's in there.