401 when attempting to confirm devise user

Question

I'm attempting to configure a devise :confirmable account, in which a user selects his password once he confirms the account (this is an officially documented modification, the details of which can be found here).

The problem: Without the modification (in which I set the password when I first create the account), the confirmation works just fine. However, under the modification I get a 401 error (unauthorized). The log of which is below:

Started POST "/users/sign_in" for 192.168.1.8 at 2016-01-31 01:53:54 -0700
Processing by Users::SessionsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"O7mUtX/5i3Cw2sgAtn8+i4VAuytkHpcxZ0ZnKL6rmfmQsRj0MblP4OGY4K3dxqXQ7qjVMsqpYEIs7Oqkm9G3JA==", "user"=>{"email"=>"neanderslob@neanderslob.com", "password"=>"[FILTERED]", "remember_me"=>"0"}, "button"=>""}
  ^[[1m^[[36mUser Load (0.8ms)^[[0m  ^[[1mSELECT  "users".* FROM "users" WHERE "users"."email" = $1  ORDER BY "users"."id" ASC LIMIT 1^[[0m  [["email", "neanderslob@neanderslob.com"]]
  ^[[1m^[[35m (0.2ms)^[[0m  BEGIN
  ^[[1m^[[36m (0.1ms)^[[0m  ^[[1mCOMMIT^[[0m
Completed 401 Unauthorized in 70ms (ActiveRecord: 1.1ms)

Of course no password was entered, as this shouldn't be necessary.

Attached is my custom ConfirmationsController

class Users::ConfirmationsController < Devise::ConfirmationsController
  # Remove the first skip_before_filter (:require_no_authentication) if you
  # don't want to enable logged users to access the confirmation page.
   skip_before_filter :require_no_authentication
   skip_before_filter :authenticate_user!

  # GET /resource/confirmation/new
  def new
    super
  end

  # POST /resource/confirmation
  def create
    super
  end

  # GET /resource/confirmation?confirmation_token=abcdef
  def show
    with_unconfirmed_confirmable do
      if @confirmable.has_no_password?
        do_show
      else
        do_confirm
      end
    end
    unless @confirmable.errors.empty?
      self.resource = @confirmable
      render 'devise/confirmations/new' #Change this if you don't have the views on default path
    end
  end

  # PUT /resource/confirmation
  def update
    with_unconfirmed_confirmable do
      if @confirmable.has_no_password?
        @confirmable.attempt_set_password(params[:user])
        if @confirmable.valid? and @confirmable.password_match?
          do_confirm
        else
          do_show
          @confirmable.errors.clear #so that we wont render :new
        end
      else
        @confirmable.errors.add(:email, :password_already_set)
      end
    end

    if !@confirmable.errors.empty?
      self.resource = @confirmable
      render 'devise/confirmations/new' #Change this if you don't have the views on default path
    end
  end


  protected

  # The path used after resending confirmation instructions.
  def after_resending_confirmation_instructions_path_for(resource_name)
    super(resource_name)
  end

  # The path used after confirmation.
  def after_confirmation_path_for(resource_name, resource)
    super(resource_name, resource)
  end


  def with_unconfirmed_confirmable
    @confirmable = User.find_or_initialize_with_error_by(:confirmation_token, params[:confirmation_token])
    if !@confirmable.new_record?
      @confirmable.only_if_unconfirmed {yield}
    end
  end

  def do_show
    @confirmation_token = params[:confirmation_token]
    @requires_password = true
    self.resource = @confirmable
    render 'devise/confirmations/show' #Change this if you don't have the views on default path
  end

  def do_confirm
    @confirmable.confirm!
    set_flash_message :notice, :confirmed
    sign_in_and_redirect(resource_name, @confirmable)
  end
end

Some wild speculation: It also might be worth mentioning that this is all being done on my localhost. This means that the url it generates is from http://localhost:3000... where my app is built to respond to a custom domain. Before the customization, I was able to just change the confirmation link from localhost:3000 over to mydomain.com:3000 and everything was alright. However I don't know if this isn't allowed under my customization (honestly don't have a deep enough knowledge to say one way or another for sure).

Anyway, thanks for any ideas you might have!

Edit: My sessions controller (the relevant controller to the error message, as was pointed out to me) is as follows... note the commented out create method

class Users::SessionsController < Devise::SessionsController

  # GET /resource/sign_in
  def new
    super
  end

  # POST /resource/sign_in
  # def create
  #   super
  # end

  # DELETE /resource/sign_out
  def destroy
    super
  end
end