diff --git a/lib/omniauth/strategies/cas/service_ticket_validator.rb b/lib/omniauth/strategies/cas/service_ticket_validator.rb
index d7117dc..82b3ce4 100644
--- a/lib/omniauth/strategies/cas/service_ticket_validator.rb
+++ b/lib/omniauth/strategies/cas/service_ticket_validator.rb
@@ -81,6 +81,7 @@ def get_service_response_body
           if http.use_ssl?
             http.verify_mode = OpenSSL::SSL::VERIFY_NONE if @options.disable_ssl_verification?
             http.ca_path = @options.ca_path
+            http.ca_file = @options.ca_file
           end
           http.start do |c|
             response = c.get "#{@uri.path}?#{@uri.query}", VALIDATION_REQUEST_HEADERS.dup