Release version 2.7.3

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.7.2

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.7.1

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.6.4

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.5.10

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.7.0

Features:
* Account deletion: Users can now delete their own accounts. Admins can
  delete any user account. Account deletion removes sessions and their
  contents created by the user and anonymizes data created through
  participation in other sessions.
* Auto-deletion: Accounts can be deleted automatically after a
  configurable period of inactivity.
* OpenID Connect: OIDC is now supported for authentication.
  Configuration discovery support is required.

Improvements:
* Public Session Pool: Added API endpoint to clone a session from the
  pool. Previously, cloning had to be performed by the client.

Bug fixes:
* Import/Export: The handling of session features during import has been
  fixed. The raw exported data can now be imported without further
  manipulation by the client.

Release version 2.6.3

Bug fixes:
* The backend now correctly responds with 4xx error codes instead of 500
  to less common errors caused by bad requests from the client-side.

Additional changes:
* Libraries have been upgraded to fix potential bugs.

Release version 2.5.9

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.6.2

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.5.8

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.6.1

Bug fixes:
* Fixed exception at startup caused by missing migration document.
* Fixed session export to correctly include all answers.

Additional changes:
* Libraries have been upgraded to fix potential bugs.

Release version 2.6.0

Features:
* Experimental support for CouchDB 2 has been added. Note: The data
  migration script is not compatible with CouchDB 2 and has to be run
  before an upgrade.

Improvements:
* Error handling and logging has been improved. It should now be easier
  to find the cause of problems. API error responses now contain the
  name of the `Exception` which caused the error. Further details for
  debugging purposes can be enabled with the new
  `api.expose-exception-messages` setting (Do NOT enable in production
  environments!).
* Updated OAuth handling to restore compatibility with 3rd-party login
  services.

Bug fixes:
* Fixed multiple bugs caused by incorrect type handling in the database
  layer.
* Fixed XFO header check behind reverse proxy (used by clients when
  embedding external websites).
* Fixed rounding error in learning progress calculation.
* Fixed `security.cors.origins` setting.
* Fixed import of data from older versions.

Security:
* Fixed DoS vulnerability in authentication handling behind reverse
  proxy.

Configuration changes:
Minor changes to the web server and Tomcat proxy configuration are
required (see [installation guide](src/site/markdown/installation.md)).

Release version 2.5.7

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.5.6

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.5.5

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.5.4

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.5.3

This is a maintenance release which only brings libraries up to date to fix
potential bugs.

Release version 2.5.2

This is a maintenance release which only brings libraries up to date to
fix potential bugs.

Release version 2.5.1

This release fixes a performance issue on session creation affecting
large installations.

Bug fixes:
* Session import works again.

Additional changes:
* Libraries have been upgraded to fix potential bugs

Release version 2.4.3

This release fixes a performance issue on session creation affecting
large installations.

Bug fixes:
* WebSocket communication now works correctly for course sessions.
  (only affects installations using the LMS connector)
* The configuration parameter `security.facebook.allowed-roles` is now
  respected.

Additional changes:
* Libraries have been upgraded to fix potential bugs