session-manager-plugin cannot be opened as macOS cannot verify the app is free from malware

[mattheworiordan]

General troubleshooting steps

• [x] I understand that if I ignore these instructions, my issue may be closed without review.
• [x] I have retried my command with --force.
• [x] I ran brew update-reset && brew update and retried my command.
• [x] I ran brew doctor, fixed as many issues as possible and retried my command.
• [x] I have checked the instructions for reporting bugs.
• [x] I made doubly sure this is not a checksum does not match error.

Description of issue

Brew cask install for AWS session manager plugin (https://formulae.brew.sh/cask/session-manager-plugin) no longer works on macOS Catalina 10.15.7 due to a security issue

Command that failed

brew cask install session-manager-plugin
session-manager-plugin # launches the window above

Output of command with --force --verbose --debug

# not relevant, the install works fine

Output of brew doctor --verbose

$ brew doctor --verbose
==> Cask Environment Variables:
BUNDLE_PATH
CHRUBY_VERSION
GEM_HOME
GEM_PATH
HOMEBREW_CASK_OPTS
LC_ALL
PATH
RBENV_VERSION
RUBYLIB
RUBYOPT
RUBYPATH
SHELL
==> $LOAD_PATHS
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/ruby-macho-2.2.0/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/rubocop-rspec-1.43.2/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/rubocop-performance-1.8.1/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/ruby-progressbar-1.10.1/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/plist-3.5.0/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/patchelf-1.3.0/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/mechanize-2.7.6/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/elftools-1.1.3/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/bindata-2.4.8/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/activesupport-6.0.3.4/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/zeitwerk-2.4.0/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/tzinfo-1.2.7/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/thread_safe-0.3.6/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/i18n-1.8.5/lib
/usr/local/Homebrew/Library/Homebrew/vendor/bundle/bundler/../ruby/2.6.0/gems/concurrent-ruby-1.1.7/lib/concurrent-ruby
/Library/Ruby/Site/2.6.0
/Library/Ruby/Site/2.6.0/universal-darwin19
/Library/Ruby/Site
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/vendor_ruby/2.6.0
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/vendor_ruby/2.6.0/universal-darwin19
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/vendor_ruby
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/universal-darwin19
/usr/local/Homebrew/Library/Homebrew
==> Homebrew Version
2.5.5-11-g90b9230
==> macOS
10.15.7
==> SIP
Enabled
==> Java
1.8.0_212
==> Homebrew Cask Staging Location
/usr/local/Caskroom
==> Homebrew Cask Taps:
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask (3675 casks)
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask-versions (161 casks)
Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry or file an issue; just ignore this. Thanks!

Warning: Some installed formulae were deleted!
You should find replacements for the following formulae:
  sshrc

Warning: You have unlinked kegs in your Cellar.
Leaving kegs unlinked can lead to build-trouble and cause brews that depend on
those kegs to fail to run properly once built. Run `brew link` on these:
  python@3.8

Output of brew tap

heroku/brew
homebrew/cask
homebrew/cask-versions
homebrew/core
homebrew/services
versent/taps

[vitorgalvao]

https://github.com/Homebrew/homebrew-cask/blob/master/doc/faq/the_app_cant_be_opened.md

Or install with --no-quarantine.