I have Ruby 1.9.3 installed on Windows 8.1
As far as I can tell the following issue remains and has been as ongoing frustration for many Windows people periodically throughout the years leading to all sorts of different synopsizes and solutions. It's just that none of them worked for me.
After installing the Heroku Toolbelt with Ruby 1.9.2 inside it I get the following error when trying to login.
Microsoft Windows [Version 6.3.9600]
(c) 2013 Microsoft Corporation. All rights reserved.
C:\WINDOWS\system32>heroku login
Enter your Heroku credentials.
Email: asdf
Password (typing will be hidden):
! Heroku client internal error.
! Search for help at: https://help.heroku.com
! Or report a bug at: https://github.com/heroku/heroku/issues/new
Error: Unable to verify certificate, please set 'Excon.defaults[:ssl_c
a_path] = path_to_certs', 'ENV['SSL_CERT_DIR'] = path_to_certs', 'Excon.defaults
[:ssl_ca_file] = path_to_file', 'ENV['SSL_CERT_FILE'] = path_to_file' or 'Excon.
defaults[:ssl_verify_peer] = false' (less secure). (Excon::Errors::SocketError)
Backtrace: C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/ssl_socket.rb:66:in 'connect'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/ssl_socket.rb:66:in 'initialize'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/connection.rb:361:in 'new'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/connection.rb:361:in 'socket'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/connection.rb:105:in 'request_call'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/middlewares/mock.rb:42:in 'request_call'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/middlewares/instrumentor.rb:22:in 'request_call'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/middlewares/base.rb:15:in 'request_call'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/middlewares/base.rb:15:in 'request_call'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/middlewares/base.rb:15:in 'request_call'
C:/Program Files (x86)/Heroku/vendor/gems/excon-0.25.3/lib/exco
n/connection.rb:244:in 'request'
C:/Program Files (x86)/Heroku/vendor/gems/heroku-api-0.3.15/lib
/heroku/api.rb:76:in 'request'
C:/Program Files (x86)/Heroku/vendor/gems/heroku-api-0.3.15/lib
/heroku/api/login.rb:9:in 'post_login'
C:/Program Files (x86)/Heroku/lib/heroku/auth.rb:80:in 'api_key
'
C:/Program Files (x86)/Heroku/lib/heroku/auth.rb:189:in 'ask_fo
r_credentials'
C:/Program Files (x86)/Heroku/lib/heroku/auth.rb:221:in 'ask_fo
r_and_save_credentials'
C:/Program Files (x86)/Heroku/lib/heroku/auth.rb:84:in 'get_cre
dentials'
C:/Program Files (x86)/Heroku/lib/heroku/auth.rb:41:in 'login'
C:/Program Files (x86)/Heroku/lib/heroku/command/auth.rb:31:in
'login'
C:/Program Files (x86)/Heroku/lib/heroku/command.rb:213:in 'run
'
C:/Program Files (x86)/Heroku/lib/heroku/cli.rb:28:in 'start'
C:/Program Files (x86)/Heroku/bin/heroku:29:in '<main>'
Command: heroku login
Version: heroku/toolbelt/3.0.0 (i386-mingw32) ruby/1.9.3