Discourse SSO Consumer for MediaWiki

DiscourseSsoConsumer is a MediaWiki extension which allows a MediaWiki site to authenticate users via the built-in SSO-provider functionality of a Discourse discussion forum.

The DiscourseSsoConsumer extension is itself a plugin for MediaWiki's PluggableAuth extension.

Installation

First, install the PluggableAuth extension. (See some configuration hints/suggestions below.)

To install DiscourseSsoConsumer:

Copy (e.g., git clone) this entire DiscourseSsoConsumer directory to your site's extensions/ directory.
Add a load-extension directive to your site's LocalSettings.php:
```
wfLoadExtension( 'DiscourseSsoConsumer' );
```
Run update.php so that a new table is added to your site's database:
```
cd YOUR-WIKI-INSTALL-DIRECTORY
cd maintenance
php update.php
```

Aside from the PluggableAuth extension (and working MediaWiki and Discourse sites), DiscourseSsoConsumer has no other dependencies.

Configuration

The complete set of configuration parameters is listed below. At a minimum, you will need to set the SsoProviderUrl and SharedSecret parameters, in concert with the Discourse site. (On the Discourse site, you will need to set enable discourse connect provider and discourse connect provider secrets under Admin -> Settings -> Login.)

As mentioned in the PluggableAuth documentation, you will likely want to configure the MediaWiki permissions to allow extensions to automatically create new local accounts for authenticated users. Add something like this to LocalSettings.php:

# Allow auth extensions to generate new local users.
$wgGroupPermissions['*']['autocreateaccount'] = true;

When DiscourseSsoConsumer loads, it will automatically plug itself into the PluggableAuth extension. You may want to tune the configuration of PluggableAuth, in particular:

$wgPluggableAuth_EnableAutoLogin
$wgPluggableAuth_EnableLocalLogin
$wgPluggableAuth_EnableLocalProperties
$wgPluggableAuth_ButtonLabelMessage

Configuration Parameters

$wgDiscourseSsoConsumer_SsoProviderUrl
- mandatory string - no default value
- Specifies the URL of the SSO provider endpoint of the Discourse server, typically of the form https://DISCOURSE-SERVER.EXAMPLE.ORG/session/sso_provider.
$wgDiscourseSsoConsumer_SharedSecret
- mandatory string - no default value
- Specifies the secret shared with the Discourse server, via its discourse connect provider secrets setting.
$wgDiscourseSsoConsumer_LinkExistingBy
- default value: [ ] (empty array)
- Array of zero or more instances of email and/or username in any order, specifying how to link Discourse credentials to existing MediaWiki accounts.
  
  DiscourseSsoConsumer keeps track of the association of Discourse user id's to MediaWiki user id's. When it encounters Discourse credentials with a novel id, it will attempt to find a matching MediaWiki user by iterating through the methods specified in LinkExistingBy. The email method will look for a matching email address. The username will look for a matching canonicalized username. If the list is exhausted without finding a match (or if no methods are specified), a new Mediawiki account will be created.
$wgDiscourseSsoConsumer_ExposeName
- default value: false
- Specifies whether or not a Discourse user's full name will be exposed to MediaWiki. The privacy controls of Discourse and MediaWiki are different and difficult to harmonize. If names are not completely public in the Discourse site policy, it is probably best not to expose them to MediaWiki at all.
  
  This setting affects the realname reported to PluggableAuth, which will by default update the realname of the account. If ExposeName is true, the local realname will be set to the name in the Discourse SSO credentials; if false, the local realname will be set to an empty string.
  
  See $wgPluggableAuth_EnableLocalProperties if you want it to leave the local realname alone completely.
$wgDiscourseSsoConsumer_ExposeEmail
- default value: false
- Specifies whether or not a user's email address will be exposed to MediaWiki. The privacy controls of Discourse and MediaWiki are different and difficult to harmonize. If names are not completely public in the Discourse site policy, it is probably best not to expose them to MediaWiki at all.
  
  This setting affects the email address reported to PluggableAuth, which will by default update the email address of the account. If ExposeEmail is true, the local email address will be set to the email address in the Discourse SSO credentials; if false, the local email address will be set to an empty string.
  
  See $wgPluggableAuth_EnableLocalProperties if you want it to leave the local email address alone completely.
$wgDiscourseSsoConsumer_GroupMaps
- optional - no default value
- Specifies how MediaWiki group memberships should be derived from Discourse credentials. If set, it should be an array of the form
```
[ 'MW-GROUP-1' => [ 'D-GROUP-X', 'D-GROUP-Y', ... ],
  'MW-GROUP-2' => [ 'D-GROUP-A', 'D-GROUP-B', ... ], ]
```
  where each entry specifies that membership in the given MediaWiki group is strictly determined by membership in at least one of the listed Discourse groups. Membership in the specified groups will be toggled according to the SSO credentials on each login; groups which are not mentioned in GroupMaps will not be touched.
  
  The two special tokens @ADMIN@ and @MODERATOR@ represent the is_admin and is_moderator flags in the SSO credentials. For example,
```
$wgDiscourseSsoConsumer_GroupMap = [ 'sysop' => [ '@ADMIN@' ],
                                     'bureaucrat' => [ '@ADMIN@' ] ];
```
  will cause a user's membership in the sysop and bureaucrat groups to be set according to the is_admin flag in the SSO credentials upon every login. Membership in any other MediaWiki groups will not be affected.
$wgDiscourseSsoConsumer_LogoutDiscourse
- default value: false
- If true, logging out of MediaWiki will also log the user out of Discourse (via a redirect to the SSO endpoint, requesting logout).

Release Notes

Version 1.0

Initial version

Version 1.0.1

Bug fix: correctly handle the delayed provision of a new user id when a new user is (auto)created in Mediawiki in response to authenticating a previously unseen Discourse user.

Known Bugs

See TODO comments in the source code.

License

This work is licensed under GPL 2.0 (or any later version).

SPDX-License-Identifier: GPL-2.0-or-later

uckelman/DiscourseSsoConsumer