Document critical changes for devs and admins in Nextcloud 22

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

admin_manual/configuration_server/email_configuration.rst

@@ -43,6 +43,8 @@ connect Nextcloud to a remote SMTP server:
 
 * Login credentials (if required)
 
+.. note:: The ``overwrite.cli.url`` parameter from ``config.php`` will be used for the SMTP EHLO.
+
 .. figure:: ../images/smtp-config-smtp.png
 
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developer_manual/app_publishing_maintenance/upgrade-guide.rst

@@ -9,11 +9,66 @@ This document will cover the most important changes in Nextcloud, as well as som
 Upgrading to Nextcloud 22
 -------------------------
 
+.. note:: Critical changes were collected `on Github <https://github.com/nextcloud/server/issues/26407>`__. See the original ticket for links to the pull requests and tickets.
+
+General
+^^^^^^^
+
+Migration commands
+******************
+
+The occ commands in the ``migration:*`` namespace are now only available in :ref:`debug mode<debug-mode>`.
+
+See `the pull request on Github <https://github.com/nextcloud/server/pull/27113>`__ for more information. If you thought you needed them, feel free to ping the author or a reviewer of the PR to solve the problem correctly. Running migrations directly mostly breaks the database status and is therefore only meant for debugging faulty migrations.
+
+Log format
+**********
+
+The JSON log format no longer contains full exception in the message field, but adds a separate exception entry is added and the existing message will only contain the exception message text. This might need adjustments by administrators when logs are extracted to external sources.
+
+Front-end changes
+^^^^^^^^^^^^^^^^^
+
+Node.js upgrade
+***************
+
+Most Nextcloud apps and Nextcloud itself is now built with Node v14 LTS instead of v12. We recommend updating the configuration of your app accordingly.
+
+IE11 removal
+************
+
+Internet Explorer 11 was phased out over the past few releases and starting with Nextcloud 22 the front-end code isn't transpiled for IE11 any longer. You may also drop IE11 from your app as core components will possibly fail with this browser anyway.
+
+Back-end changes
+^^^^^^^^^^^^^^^^
+
 Removed support for database.xml
 ********************************
 
 The support for an app's ``appinfo/database.xml`` has been removed.
 
+
+LDAP factory availability
+*************************
+
+``\OCP\LDAP\ILDAPProviderFactory`` received a new method ``isAvailable`` so apps can check if LDAP is configured and used before any attributes are fetched or similar.
+
+Boolean database columns
+************************
+
+Since Oracle can not store booleans in a non-nullable boolean column Nextcloud doesn't support non-null boolean columns anymore. Apps have to migrate their schema to nullable boolean columns.
+
+
+HTTP 401 for invalid username/password
+**************************************
+
+When invalid username/password is sent to a Nextcloud API, Nextcloud will now respond with a HTTP 401 status instead of 403.
+
+
+Removed APIs
+************
+* ``\OCP\User``
+
 Upgrading to Nextcloud 21
 -------------------------
 

developer_manual/digging_deeper/debugging.rst

@@ -2,6 +2,8 @@
 Debugging
 =========
 
+.. _debug-mode:
+
 Debug mode
 ----------