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By David Patrick
Troubleshooting tips for using Rails with Auth0.We recommend that you log in to follow this quickstart with examples configured for your account.

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Troubleshooting

The following are troubleshooting topics that you might run into when using the Rails quickstart.

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Using a reverse proxy

The redirect_uri parameter that OmniAuth generates when redirecting to login is based on the Host header that is passed to Rails. This can cause incorrect callback URLs to be passed when using this strategy (and OmniAuth in general) with a reverse proxy. You can adjust the host used by OmniAuth with the following snippet: 
OmniAuth.config.full_host = lambda do |env|
    scheme         = env['rack.url_scheme']
    local_host     = env['HTTP_HOST']
    forwarded_host = env['HTTP_X_FORWARDED_HOST']
    forwarded_host.blank? ? "#{scheme}://#{local_host}" : "#{scheme}://#{forwarded_host}"
end
See this StackOverflow thread for more information.

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ActionController::InvalidAuthenticityToken

This is likely caused by a missing CSRF token needed to POST the login request. If you inspect the login button in your browser, you should see something like this: 
<a data-method="post" href="auth/auth0">Login</a>
… and in the <head> element for the page, you should have CSRF meta tags like these: 
<meta name="csrf-param" content="authenticity_token">
<meta name="csrf-token" content="UY2XpKwxzwBWalxFVJ8yKsao/33it7If09BnZewpHifVPSpFJd2LrA7xgQn6VQrhZNGjgZoLI3kV+bkQHtr+Rw==">
With those elements in place, Rails will convert the login link to POST the CSRF token to the backend to verify it before redirecting to login.

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ActionDispatch::Cookies::CookieOverflow

This error means that a cookie session is being used and because the whole profile is being stored, it overflows the max-size of 4 kb. If you are unable to access the user profile, or you get an error similar to NoMethodError, undefined method '[]' for nil:NilClass, try using In-Memory store for development. Go to /config/initializers/session_store.rb (or create it if it does not exist) and add the following: 
Rails.application.config.session_store :cache_store
Go to /config/environments/development.rb and add the following: 
config.cache_store = :memory_store
Restart your Rails server for these changes to take effect. It is recommended that a memory store, such as MemCached, is being used for production applications.

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SSL Issues

Under some configurations, Ruby may not be able to find certification authority certificates (CA certs). Download the CA certs bundle to the project directory: 
curl -L -o lib/ca-bundle.crt http://curl.haxx.se/ca/ca-bundle.crt
Add this initializer to config/initializers/fix_ssl.rb: 
# config/initializers/fix_ssl.rb

require 'open-uri'
require 'net/https'

module Net
  class HTTP
    alias_method :original_use_ssl=, :use_ssl=

    def use_ssl=(flag)
      path = ( Rails.env == "development") ? "lib/ca-bundle.crt" : "/usr/lib/ssl/certs/ca-certificates.crt"
      self.ca_file = Rails.root.join(path).to_s
      self.verify_mode = OpenSSL::SSL::VERIFY_PEER
      self.original_use_ssl = flag
    end
  end
end

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“failure message=invalid_credentials”

This issue doesn’t occur when working locally but may happen in a staging or production environment. The error message may be displayed as: 
omniauth: (auth0) Authentication failure! invalid_credentials: OAuth2::Error, server_error: The redirect URI is wrong. You send [wrong url], and we expected [callback url set in your app settings]
To solve this, add the following to config/environments/staging.rb or production.rb: 
OmniAuth.config.full_host = "http://www.example.com"
Substitute http://www.example.com with the actual URL you’ll be using in your application. Edit on GitHub