CSRF protection support

[miguelgrinberg]

Fixes #321

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1c7020c) to head (323e81d).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #330   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           15        16    +1     
  Lines         1601      1669   +68     
  Branches       287       300   +13     
=========================================
+ Hits          1601      1669   +68     

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