Fix session cookie being recreated on every export

[rfontanarosa]

closes #1160

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.62%. Comparing base (8d8f16e) to head (4b30bd9).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2471      +/-   ##
==========================================
+ Coverage   59.38%   59.62%   +0.24%     
==========================================
  Files         113      113              
  Lines        2797     2804       +7     
  Branches      421      423       +2     
==========================================
+ Hits         1661     1672      +11     
+ Misses       1074     1070       -4     
  Partials       62       62              

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