feat(auth): when user is not logged in, failure to access a dashboard should redirect to login screen

[sfirke]

SUMMARY

If a viewer is not logged in, or they are the public/anonymous user, and they click a link that takes them to a Superset dashboard that is not public, they are currently told "You don't have access" and sent to the list of dashboards, where they will see only public ones listed. This is often misleading: in most cases, the problem is not that they don't have access -- they just need to log in.

After the PR, such cases are routed to the login screen, and after a successful login the users are sent back to the dashboard they were trying to access.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

BEFORE

current_redirect.mp4

AFTER

redirect_new.mp4

note I've changed the error message since recording this

TESTING INSTRUCTIONS

Create a dashboard with restricted access, try to view it while not logged in.

ADDITIONAL INFORMATION

Implements this feature request: #22190
Replaces this stale PR: #23280

I have the DASHBOARD_RBAC flag enabled as well as the Public role in use. My code alterations are minimal so I don't think it will negatively affect deployments that differ from mine, but it would be good to have someone check.

I'm not sure how to write tests for this but am open to it if someone can advise.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.90%. Comparing base (76d897e) to head (d8ad102).
Report is 774 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #30380       +/-   ##
===========================================
+ Coverage   60.48%   83.90%   +23.41%     
===========================================
  Files        1931      533     -1398     
  Lines       76236    38524    -37712     
  Branches     8568        0     -8568     
===========================================
- Hits        46114    32322    -13792     
+ Misses      28017     6202    -21815     
+ Partials     2105        0     -2105     

Flag	Coverage Δ
hive	48.99% <0.00%> (-0.18%)	⬇️
javascript	?
mysql	76.88% <100.00%> (?)
postgres	76.95% <100.00%> (?)
presto	53.49% <0.00%> (-0.32%)	⬇️
python	83.90% <100.00%> (+20.41%)	⬆️
sqlite	76.40% <100.00%> (?)
unit	60.64% <0.00%> (+3.01%)	⬆️

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[villebro]

LGTM with a non-blocking question on the next url param.