This change is going to be backported to v1.x.x to have a good migration path.
Bearer auth with API_CLIENTS config key is deprecated and planned to be
removed in v2.0.0.

* Removal of ldapalchemy and LDAP mocking support
* Removal of dependency on ldap3 (except for the migration)
* Remaining "LDAP_<name>" config keys are renamed to "<name>"
* Web interface to create, edit and delete groups
* Consistent foreign key, cascading and nullable configuration on all models
* User/Group.dn is replaced with numeric User/Group.id
* User.uid is renamed to User.unix_uid (to differentiate with new User.id)
* Group.gid is renamed to Group.unix_gid (to differentiate with new Group.id)
* All User/Group/Mail related routes now use the database ids instead of uid/gid/dn
* PasswordToken/MailToken now reference users directly instead of storing loginnames

The database migration (optionally) uses the v1 config keys to connect to
an LDAP server and to import all users, groups and mail forwardings.

Fixes #114

Regression was introduced by 45d4598e (Replace flask_oauthlib with plain
oauthlib). Support for HTTP Basic authentication scheme for client
authentication is actually required by RFC6749.

Fixes #115

Regression was introduced by 45d4598e (Replace flask_oauthlib with plain oauthlib).

Existing links continue to work. However support for legacy links (without id)
is deprecated and will be removed in the future.

This affects mail verification and password reset links. Existing links
continue to work. However support for legacy links (without id) is
deprecated and will be removed in the future.

Existing invite links continue to work. However support for legacy links
(without id) is deprecated and will be removed in the future.

Fixes #104.

Replaced "group" keyword argument for login_required with "permission_check".
Most views already define a *_acl_check function that returns whether the
current user has the required permissions for use with register_navbar. The
same function can now be passed to login_required as the "permission_check"
argument.

Differenciated login and selfservice access permissions. Previously
ACL_SELFSERVICE_GROUP was required to login. Now ACL_ACCESS_GROUP is required
to login and ACL_SELFSERVICE_GROUP is required to access selfservice functions
(and to use role-granting invite links). A user with just ACL_ACCESS_GROUP can
now login, access the services overview page and authenticate with OAuth2
services he has access to, but not change his user attributes, password or
roles/permissions.

Fixes #26.

The test cases effectivly tested if the user_acl_check works which is already
covered by other test cases.

Prior to this change permission errors (i.e. the user is logged in but does
not have a required group) were reported with flash('Access denied') and a
redirect to the selfservice index page. This causes two problems: The error
is reported with HTTP status 301/200 which is difficult to check for in tests.
This can also cause redirect loops as soon as the selfservice uses more
differentiated permission checks (see #104).

With this change a dedicated error page is displayed in place the requested
page and the HTTP status 403 is returned. This is implemented with
flask's errorhandler concept for 403.

flask_oauthlib is no longer available in Debian Bullseye. It is only a
wrapper around oauthlib, which is still available. While this change does
increase the OAuth2 code size, it achieves compatability with both Debian
Buster and Bullseye.

Aside from error handling, this change has no noticable effects on OAuth2.0
clients. In terms of error handling, a few cases that were not properly
handled before now return appropriate error pages.

Fixes #101

Prior to this change user passwords were not validated on change aside from
their length, but validated on login/bind by ldap3 with SASLprep. Instead of
using SASLprep on password change, this change restricts passwords to 7-bit
ASCII without control characters. Control characters are forbidden by
SASLprep. Multi-byte characters are uncommon in password, especially in those
generated by password managers. This ensures that passwords are always
SASLprep-safe without implementing the rather complex SASLprep algorithm. It
also allows us to fully describe the alphabet restrictions in the relevant
forms.

Fixes #100

Ldap3 raises LDAPSASLPrepError on bind if the password contains characters
forbidden by SASLPrep (string preperation/normalization algorithm for user
names and passwords). Examples are carriage return ("\r") or newline ("\n")
characters. See #100.

For password reset this prevents circumventing the loginname/email-based
ratelimit.

Co-authored-by: psy <psy@darmstadt.ccc.de>