MongooseIM: Add documentation.

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [unreleased]
 ### Added
+- [MongooseIM](https://github.com/esl/MongooseIM) http authentication support.
 - LDAP authentication
 - External OAuth provider authentication
 - A [job queue](https://git.pleroma.social/pleroma/pleroma_job_queue) for federation, emails, web push, etc.

docs/config/howto_mongooseim.md

@@ -0,0 +1,10 @@
+# Configuring MongooseIM (XMPP Server) to use Pleroma for authentication
+
+If you want to give your Pleroma users an XMPP (chat) account, you can configure [MongooseIM](https://github.com/esl/MongooseIM) to use your Pleroma server for user authentication, automatically giving every local user an XMPP account.
+
+In general, you just have to follow the configuration described at [https://mongooseim.readthedocs.io/en/latest/authentication-backends/HTTP-authentication-module/](https://mongooseim.readthedocs.io/en/latest/authentication-backends/HTTP-authentication-module/) and do these changes to your mongooseim.cfg.
+
+1. Set the auth_method to `{auth_method, http}`.
+2. Add the http auth pool like this: `{http, global, auth, [{workers, 50}], [{server, "https://yourpleromainstance.com"}]}`
+
+Restart your MongooseIM server, your users should now be able to connect with their Pleroma credentials.