Submit an ASP.net form by clicking a WebForm link using Mechanize.

example.rb

require 'mechanize'

# Fetch the home page
browser = Mechanize.new
home_page = browser.get('https://www.example-aspnet-site.com/')

# Fill out the login form
login_form = home_page.forms.first
login_form.field_with(:name => /UserName/i).value = ARGV[0]
login_form.field_with(:name => /Password/i).value = ARGV[1]
user_dashboard = home_page.link_with(:text => /Login/).click

mechanize_page_link.rb

class Mechanize::Page::Link
  def click
    if self.href =~ /WebForm/ && form = self.page.form_with(:name => /aspnetForm/)
      form['__EVENTTARGET'], form['__EVENTARGUMENT'] = self.attributes['href'].scan(/["']([^"']*)["']/).flatten
      form.submit
    else
      super
    end
  end
end