Add allow origins field to CORS spec

[stefanprodan]

Fix: #603

[codecov-commenter]

Codecov Report

Merging #604 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #604   +/-   ##
=======================================
  Coverage   55.00%   55.00%           
=======================================
  Files          62       62           
  Lines        5303     5303           
=======================================
  Hits         2917     2917           
  Misses       1959     1959           
  Partials      427      427           

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