OmniAuth v2 Shibboleth provider strategy

OmniAuth v2 Shibboleth strategy is an OmniAuth v2 strategy for authenticating through Shibboleth provider (SAML). If you do not know OmniAuth, please visit OmniAuth wiki.

https://github.com/omniauth/omniauth/wiki

The detail of the authentication middleware Shibboleth is introduced in Shibboleth wiki.

https://wiki.shibboleth.net/

OmniAuth basically works as a middleware of Rack applications. It provides environment variable named 'omniauth.auth' (auth hash) after authenticating a user. The 'auth hash' includes the user's attributes. By providing user attributes in the fixed format, applications can easily implement authentication function using multiple authentication methods.

OmniAuth Shibboleth provider strategy uses the 'auth hash' for providing user attributes passed by Shibboleth SP. It enables developers to use Shibboleth provider and the other authentication methods, including local auth, together in one application.

gem 'omniauth-v2-shibboleth-provider'

To use OmniAuth Shibboleth provider strategy as a middleware in your rails application, add the following file to your rails application initializer directory.

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth
end

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, {
    :shib_session_id_field     => "Shib-Session-ID",
    :shib_application_id_field => "Shib-Application-ID",
    :debug                     => false,
    :extra_fields => [
      :"unscoped-affiliation",
      :entitlement
    ]
  }
end

In the above example, 'unscoped-affiliation' and 'entitlement' attributes are additionally provided in the raw_info field. They can be referred like request.env["omniauth.auth"]["extra"]["raw_info"]["unscoped-affiliation"]. The detail of the omniauth auth hash schema is described in the following page.

https://github.com/omniauth/omniauth/wiki/Auth-Hash-Schema

'eppn' attribute is used as uid field. 'displayName' attribute is provided as request.env["omniauth.auth"]["info"]["name"].

These can be changed by :uid_field, :name_field option. You can also add any "info" fields defined in Auth-Hash-Schema by using :info_fields option.

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, {
    :uid_field                 => "uid",
    :name_field                => "displayName",
    :info_fields => {
      :email    => "mail",
      :location => "contactAddress",
      :image    => "photo_url",
      :phone    => "contactPhone"
    }
  }
end

In the previous example, Shibboleth provider strategy does not pass any :info fields and use 'uid' attribute as uid fields.

If you need more flexible attribute definition, you can use lambda (Proc) to define your attributes. In the following example, 'uid' attribute is chosen from 'eppn' or 'mail', 'info'/'name' attribute is defined as a concatenation of 'cn' and 'sn' and 'info'/'affiliation' attribute is defined as 'affiliation'@my.localdomain. 'request_param' parameter is a method defined in OmniAuth::Shibboleth::Strategy. You can specify attribute names by downcase strings in either request_type, :env, :header and :params.

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, {
    :uid_field                 => lambda {|request_param| request_param.call('eppn') || request_param.call('mail')},
    :name_field                => lambda {|request_param| "#{request_param.call('cn')} #{request_param.call('sn')}"},
    :info_fields => {
      :affiliation => lambda {|request_param| "#{request_param.call('affiliation')}@my.localdomain"},
      :email    => "mail",
      :location => "contactAddress",
      :image    => "photo_url",
      :phone    => "contactPhone"
    }
  }
end

When you use omniauth with devise, the omniauth configuration is applied before devise configuration and some part of the configuration overwritten by the devise's. It may not work as you assume. So thus, in that case, currently you should write your configuration only in device configuration.

config/initializers/devise.rb:

config.omniauth :shibboleth, {:uid_field => 'eppn',
                         :info_fields => {:email => 'mail', :name => 'cn', :last_name => 'sn'},
                         :extra_fields => [:schacHomeOrganization]
                  }

The detail is discussed in the following thread.

heartcombo/devise#2128

In your application, simply direct users to '/auth/shibboleth' to have them sign in via your company's Shibboleth SP and IdP. '/auth/shibboleth' url simply redirect users to '/auth/shibboleth/callback', so thus you must protect '/auth/shibboleth/callback' by Shibboleth SP.

Example shibd.conf:

<Location /application_path/auth/shibboleth/callback>
  AuthType shibboleth
  ShibRequestSetting requireSession 1
  require valid-user
</Location>

Shibboleth provider strategy just checks the existence of Shib-Session-ID or Shib-Application-ID.

If you want to use omniauth-v2-shibboleth without Apache or IIS, you can try rack-saml. It supports a part of Shibboleth SP functions.

https://github.com/toyokazu/rack-saml

Shibboleth provider strategy assumes the attributes are provided via environment variables because the use of ShibUseHeaders option may cause some problems. The details are discussed in the following page:

https://wiki.shibboleth.net/confluence/display/SHIB2/NativeSPSpoofChecking

To provide Shibboleth attributes via environment variables, we can not use proxy based approach, e.g. mod_proxy_balancer. Currently we can realize it by using Phusion Passenger as an application container. An example construction pattern is shown in presence_checker application (https://github.com/toyokazu/presence_checker/).

You understand the issues using ShibUseHeaders, but and yet if you want to use the proxy based approach, you can use :request_type option. This option enables us to specify what kind of parameters are used to create 'omniauth.auth' (auth hash). This option can also be used to develop your Rails application without local IdP and SP by using :params option. The option values are:

• :env (default) The environment variables are used to create auth hash.
• :header The auth hash is created from header vaiables. In the Rack middleware, since header variables are treated as environment variables like HTTP_, the specified variables are converted as the same as header variables, HTTP_. This :request_type is basically used for mod_proxy_balancer approach.
• :params The query string or POST parameters are used to create auth hash. This :request_type is basically used for development phase. You can emulate SP function by providing parameters as query string. In this case, please do not forget to add Shib-Session-ID or Shib-Application-ID value which is used to check the session is created at SP.

The following is an example configuration.

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, { :request_type => :header }
end

If you use proxy based approach, please be sure to add ShibUseHeaders option in mod_shib configuration.

<Location /secure>
  AuthType shibboleth
  ShibRequestSetting requireSession 1
  ShibUseHeaders On
  require valid-user
</Location>

When you deploy a new application, you may want to confirm the assumed attributes are correctly provided by Shibboleth SP. OmniAuth Shibboleth provider strategy provides a confirmation option :debug. If you set :debug true, you can see the environment variables provided at the /auth/shibboleth/callback uri.

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, { :debug => true }
end

If your application want to receive multiple values as one attribute, Shibboleth passes them as follows:

user2@example2.com;user1@example1.com;user3@example3.com

If your application only wants the first entry sorted by alphabetical order, you can use flexible attribute configuration as follows (since semicolons in attribute values are escaped with a backslash, escaped semicolons are skiped for splitting):

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, {
    :info_fields => {
      :email    => lambda {|request_param| request_param.call('email').split(/(?<!\\);/).sort[0]}
    }
  }
end

However, if you use device to integrate omniauth, lambda function cannot be used. In such a situation, if you still think that attribute conversions in the middleware is required, you can use :multi_values option.

• :raw (default) Raw multiple values are passed to the application.
• :first The first entry of multiple values is passed to the application.
• lambda function The other descriptions are regarded as lambda function written in String form. The string will be evaluated as Ruby code and used for processing multiple values in the attribute.

If you specify :first, you can obtain user2@example.com in the above example.

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, {
    :multi_values => :first
  }
end

If you need the first attribute in alphabetical order, you can specify lambda function in String form as follows:

% vi config/initializer/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shibboleth, {
    :multi_values => 'lambda {|param_value| param_value.nil? ? nil : param_value.split(/(?<!\\\\);/).sort[0]}'
  }
end

omniauth-v2-shibboleth is released under the MIT license.

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