Shibboleth OmniAuth Provider

NOTE: Note: The preferred approach for integrating a Shibboleth authentication system with GitLab 10 or newer is to use GitLab's SAML integration. This documentation is for Omnibus GitLab 9.x installs or older.

In order to enable Shibboleth support in GitLab we need to use Apache instead of NGINX (It may be possible to use NGINX, however this is difficult to configure using the bundled NGINX provided in the Omnibus GitLab package). Apache uses mod_shib2 module for Shibboleth authentication and can pass attributes as headers to OmniAuth Shibboleth provider.

To enable the Shibboleth OmniAuth provider you must configure Apache Shibboleth module. The installation and configuration of the module itself is out of the scope of this document. Check https://wiki.shibboleth.net/confluence/display/SP3/Apache for more information.

You can find Apache config in GitLab Recipes.

The following changes are needed to enable Shibboleth:

Protect OmniAuth Shibboleth callback URL:

<Location /users/auth/shibboleth/callback>
  AuthType shibboleth
  ShibRequestSetting requireSession 1
  ShibUseHeaders On
  require valid-user
</Location>

Alias /shibboleth-sp /usr/share/shibboleth
<Location /shibboleth-sp>
  Satisfy any
</Location>

<Location /Shibboleth.sso>
  SetHandler shib
</Location>

Exclude Shibboleth URLs from rewriting. Add RewriteCond %{REQUEST_URI} !/Shibboleth.sso and RewriteCond %{REQUEST_URI} !/shibboleth-sp. Config should look like this:
```
# Apache equivalent of Nginx try files
RewriteEngine on
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !/Shibboleth.sso
RewriteCond %{REQUEST_URI} !/shibboleth-sp
RewriteRule .* http://127.0.0.1:8080%{REQUEST_URI} [P,QSA]
RequestHeader set X_FORWARDED_PROTO 'https'
```
NOTE: Starting from GitLab 11.4, OmniAuth is enabled by default. If you're using an earlier version, you'll need to explicitly enable it in /etc/gitlab/gitlab.rb.
In addition, add Shibboleth to /etc/gitlab/gitlab.rb as an OmniAuth provider. User attributes will be sent from the Apache reverse proxy to GitLab as headers with the names from the Shibboleth attribute mapping. Therefore the values of the args hash should be in the form of "HTTP_ATTRIBUTE". The keys in the hash are arguments to the OmniAuth::Strategies::Shibboleth class and are documented by the omniauth-shibboleth gem (take care to note the version of the gem packaged with GitLab). If some of your users appear to be authenticated by Shibboleth and Apache, but GitLab rejects their account with a URI that contains "e-mail is invalid" then your Shibboleth Identity Provider or Attribute Authority may be asserting multiple e-mail addresses. In this instance, you might consider setting the multi_values argument to first.

The file should look like this:
```
external_url 'https://gitlab.example.com'
gitlab_rails['internal_api_url'] = 'https://gitlab.example.com'

# disable Nginx
nginx['enable'] = false

gitlab_rails['omniauth_allow_single_sign_on'] = true
gitlab_rails['omniauth_block_auto_created_users'] = false
gitlab_rails['omniauth_providers'] = [
  {
    "name"  => "'shibboleth"',
    "label" => "Text for Login Button",
    "args"  => {
        "shib_session_id_field"     => "HTTP_SHIB_SESSION_ID",
        "shib_application_id_field" => "HTTP_SHIB_APPLICATION_ID",
        "uid_field"                 => 'HTTP_EPPN',
        "name_field"                => 'HTTP_CN',
        "info_fields" => { "email" => 'HTTP_MAIL'}
    }
  }
]
```
Reconfigure or restart GitLab for the changes to take effect if you installed GitLab via Omnibus or from source respectively.

On the sign in page, there should now be a "Sign in with: Shibboleth" icon below the regular sign in form. Click the icon to begin the authentication process. You will be redirected to IdP server (depends on your Shibboleth module configuration). If everything goes well the user will be returned to GitLab and will be signed in.

Apache 2.4 / GitLab 8.6 update

The order of the first 2 Location directives is important. If they are reversed, you will not get a Shibboleth session!

<Location />
  Require all granted
  ProxyPassReverse http://127.0.0.1:8181
  ProxyPassReverse http://YOUR_SERVER_FQDN/
</Location>

<Location /users/auth/shibboleth/callback>
  AuthType shibboleth
  ShibRequestSetting requireSession 1
  ShibUseHeaders On
  Require shib-session
</Location>

Alias /shibboleth-sp /usr/share/shibboleth

<Location /shibboleth-sp>
  Require all granted
</Location>

<Location /Shibboleth.sso>
  SetHandler shib
</Location>

RewriteEngine on

#Don't escape encoded characters in api requests
RewriteCond %{REQUEST_URI} ^/api/v4/.*
RewriteCond %{REQUEST_URI} !/Shibboleth.sso
RewriteCond %{REQUEST_URI} !/shibboleth-sp
RewriteRule .* http://127.0.0.1:8181%{REQUEST_URI} [P,QSA,NE]

#Forward all requests to gitlab-workhorse except existing files
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f [OR]
RewriteCond %{REQUEST_URI} ^/uploads/.*
RewriteCond %{REQUEST_URI} !/Shibboleth.sso
RewriteCond %{REQUEST_URI} !/shibboleth-sp
RewriteRule .* http://127.0.0.1:8181%{REQUEST_URI} [P,QSA]

RequestHeader set X_FORWARDED_PROTO 'https'
RequestHeader set X-Forwarded-Ssl on

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Shibboleth OmniAuth Provider

Apache 2.4 / GitLab 8.6 update

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