Catching failed OmniAuth login attempt information in Rails 4 application - ruby-on-rails-4

Question

Goal: I'm trying to get a Ruby on Rails application to send me emails whenever a user fails to log into OmniAuth. I want the e-mail to include (1) the username entered in the form, and (2) an MD5 hash of the password field.
Obstacle: OmniAuth returns a POST after a successful login, and a GET after an authentication failure. The "success" POST includes the username and a filtered password, but the "fail" GET does not include these two parameters.
So I guess my question is "Can I make OmniAuth return the parameters I want? If not, how can I make Rails remember the form data after it gets POST'ed to OmniAuth?"

Answer 1

I emailed the OmniAuth team and they gave me the solution below (thank you so much!):
You can do custom failure handling by adding an on_failure action.
OmniAuth.config.on_failure = Proc.new { |env| #do stuff }
https://github.com/intridea/omniauth/blob/master/lib/omniauth/failure_endpoint.rb
is the default failure endpoint as an example
So I added the following in config/initializers/omniauth.rb:
OmniAuth.config.on_failure = Proc.new{|env|
myLog = ActiveSupport::TaggedLogging.new(Logger.new("log/omniauth_log.txt"))
myLog.tagged("OmniAuth", "ENV") { myLog.info "Failed login attempt - username: #{env["rack.request.form_hash"]["username"]}, password: #{env["rack.request.form_hash"]["password"]} "}
OmniAuth::FailureEndpoint.new(env).redirect_to_failure}
...and it records the username and password correctly. All that's left to do is encrypt the password.
If you want to display everything that's going on, you can log #{env.inspect} itself. It's a very large hash though (that also contains smaller hashes), so maybe log #{env.inspect} once and pick out the fields relevant to your task.