This only works when you actually have a session ID (not the case for Rails' CookieStore, for example):

request.session_options[:id]
# => "142b17ab075e71f2a2e2543c6ae34b94"

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

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Read more Show archive.org snapshot

Note that it's a bad idea to expose your session ID, so be careful what you use this for.