Closes #163

Prerequisite for implementing missing OIDC features.

Prerequisite for doing the same to OAuth2 state. This is required for
implementing missing OIDC features later.

Limited to OpenID provider conformance profiles "Basic" and "Config":

- Support for features mandatory to implement for all OpenID Providers,
  not the feature set for Dynamic OpenID Providers
- Only Authorization Code Flow, no support for Implicit/Hybrid Flow
- Only code response type, no support for token/id_token
- Server metadata is served at /.well-known/openid-configuration

Additional/optional features:

- Support for "claims" parameter
- Support for standard scopes "profile" and "email"
- Support for non-standard scope/claim "groups" (in violation of RFC 9068)

Compatability with existing (working) uffd client setups: Authorization
requests without the "openid" scope behave the same as before  Prior to this
change authorization requests with the "openid" scope were rejected by uffd.

This change adds direct dependencies to pyjwt and cryptography. Prior to this
change both were already transitive dependencies of oauthlib.

SQLAlchemy v1.4 (Debian Bookworm) annoyingly warns about overlapping
user/mfa_method relationships.

Fixes #146

9bfd6f81 changed the format of authorization codes, but did not adapt the
invalidation code accordingly. Because of this, authorization codes were
not invalidated and could have been used multiple times to request access
tokens until expiring.

Time-based one-time password (TOTP) codes are only valid for a short period
of time. In addition they are meant to be single-use to make them more
resistant against phishing and eavesdropping (e.g. keyloggers). Prior to this
change uffd did not keep track of used codes and thus did not prevent code
reuse.

- Add CI tests for Bookworm
- Disable pylint deprecation warnings for crypt
- Mitigate Flask changes that broke a few tests
- Set create_constraint=True for Booleans/Enums to mitigate SQLAlchemy changes
- Mitigate new Alembic CHECK constraint behaviour in batch mode

This setting is more flexible than the existing REMAILER_LIMIT_TO_USERS config
option. The config option is therefore deprecated and will be removed in the
next major version.

Turns check_migrations.py into a normal test case. Speeds up pipeline by
making html5validator use the artifacts from tests:buster:sqlite instead of
running the tests on its own.

Uffd now requires that MariaDB databases have utf8mb4 charset and
utf8mb4_nopad_bin collation. The collation was chosen for consistency with
SQLite's BINARY collation.

Previously Unix UIDs/GIDs were allocated by using the highest used ID + 1.
This caused ID reuse when the newest user/group was deleted. In addition, the
implementation did not work on MariaDB (at all, it was not possible to create
users/groups).

The new approach accounts for all IDs ever used regardless of whether or not
users/groups are deleted. It always allocates the lowest ID in the configured
range that was never used.

Aside from the different allocation algorithm, this change introduces a
generic locking mechanism and prerequisites for testing migration scripts.

Enforces uniqueness of (verified) email addresses across all users. Email
addresses are compared case-insensitivly and Unicode-normalized. The new
unique constraints are disabled by default and can be enabled with a CLI
command. They are planned to become mandatory in uffd v3.

A lot of software does not allow multiple users to share the same email
address. This change prevents problems with such software.

To enable this feature run the command:

  uffd-admin unique-email-addresses enable

The commands reports any issues (e.g. existing duplicate addresses) that
prevent enabling the feature.

This change also introduces a generic mechanism to store feature flags in the
database and improves error handling for login name constraint violations.

Restructure tests into views/models/commands subdirectories to mirror the new
source tree structure introduced with ac731bf4 (Restructure source tree).

Deprecates old case-sensitive format. Some software out there stores email
addresses converted to lower case, breaking v1 remailer addresses. The new
format is case-insensitive and generally more robust.

Uffd continues to use and support the v1 format for services setup before
this change. Support for the old format is planned to be remove in uffd v3.
It is possbile to gradually migrate services to the new format with a service
setting in the admin interface.

Also fixes compatability issue with very recent SQLAlchemy versions introduced
by b391e176 (whens parameter of case function).

Also fixes a minor email-related bug in the admin interface and bad
texts/translations in the selfservice UI.

Access control is done via normal api credentials.
See README.md for details.
Adds an optional dependency on python3-prometheus-client.

Preperation for future features that require per-service user settings
or state, e.g. stateful sync or service-specific email settings.

The additional JOIN of ServiceUser degrades getusers API performance
by 30-50%. For API calls that return many users, this is compensated by
an otherwise unrelated optimization (selectinload instead of joinedload).

Convert DateTime fields to UTC, use "utcnow" instead of "now" and use
babel helper/filter when dates/times are displayed or parsed from user
input.

Uffd continues to use the system's timezone in the user interface by
default.  However, it is now possible to overwrite this with the
BABEL_DEFAULT_TIMEZONE config option.

Unittest jobs now fail if any test fails. Unittests on Bullseye no longer
fail due to jinja2 import errors. Linter jobs run faster.

Move all models, views, cli commands and templates into corresponding
top-level folders. Detailed changes:

- uffd/<NAME>/models.py -> uffd/models/<NAME>.py
- uffd/<NAME>/cli.py -> uffd/commands/<NAME>.py
- uffd/<NAME>/views.py -> uffd/views/<NAME>.py
- uffd/<NAME>/templates/* -> uffd/templates/
- uffd/ratelimit.py -> uffd/models/ratelimit.py (it contains models)
- gendevcert from uffd/__init__.py -> uffd/commands/gendevcert.py
- profile from uffd/__init__.py -> uffd/commands/profile.py
- cleanup from uffd/tasks.py -> uffd/commands/cleanup.py
- roles-update-all from uffd/role/views.py -> uffd/commands/...
- Views from uffd/__init__.py -> uffd/views/__init__.py
- All models can/should be imported from uffd.models
- flask shell auto-imports all models instead of only a few

The old structure was meant to keep the code modular and related
code/resources close to each other. However, the modules turned out to
be heavily interdependent and not very modular. Also importing was fragile
due to ordering issues.

With the new structure the dependency tree is much simpler: Infrastructure
code (top-level *.py files) has no internal dependencies. Models only
depend on infrastructure and other models. Views and cli commands depend
on infrastructure, models and other views/commands.

Going forward there is still some restructuring to do, e.g.:

- Move mfa setup views to selfservice views
- Move mfa auth views to session views
- Move utility code from views to infrastructure (e.g. login_required)
- In most cases views should not need to import from other views
- Reorganize infrastructure code

With this feature, uffd can be configured to hide mail addresses of users
from certain services while still allowing the services to send mails to the
users.

To these services uffd returns special remailer addresses instead of the real
mail addresses. When a service sends an email to a remailer address the mail
server queries uffd's API and replaces the remailer address with the real mail
address in both envelope and headers.

This feature requires additional mail server configuration (Postfix
canonical_maps) and support in uffd-socketmapd.

When the "new invite" page was submitted with e.g. an invalid "Valid Until"
value, uffd displayed an error and reset the whole form. This was confusing
to users.

Now the form content is preserved on errors. Also the "Valid Until" field now
has min/max attributes to prevent submitting the form with invalid values.

Fixes #134

The group and role update subcommands set the description to an empty string
if the "--description" option was ommitted.

Fixes #156

When the service overview was introduced, it was meant to be optional. Thus
if the SERVICES config option was empty (the default), uffd returned 404.

Commit fa67bde0 (Migrate OAuth2 and API clients to database) introduced the
regression that accessing the service overview page when no services are
visible based on the permissions of the current user (or guest if not logged
in), 404 is returned.

This change fixes the regression and further changes the behavior to improve
consistency. Since fa67bde0, the page is relevant to admin users regardless of
the SERVICES config option. Therefore uffd asks for login or reports missing
permissions in all cases it originally returned 404.

Also adds a shallow Service model that coexists with the config-defined
services to group multiple OAuth2 and API clients together.

Clients defined in the config with OAUTH2_CLIENTS and API_CLIENTS_2 are
imported by the database migrations.

Removes support for complex values for the OAuth2 client group_required option.
Only simple group names are supported, not (nested) lists of groups previously
interpreted as AND/OR conjunctions. Also removes support for the login_message
parameter of OAuth2 clients.

The generation now happens in a subquery inside the INSERT statement instead
of separate client-managed query. This should also reduce the risk of race
conditions.

Service and non-service users may now use the same UID range.

The command replaces all existing mechanisms for deleting expired objects. It
should run at least daily. The Debian package includes a corresponding cron
job.

Ratelimit events now use UTC timestamps instead of localtime. On upgrade all
past ratelimit events are cleared.

Argon2 is a modern password hashing algorithm. It is significantly more secure
than the previous algorithm (salted SHA512). User logins with Argon2 are
relativly slow and cause significant spikes in CPU and memory (100MB) usage.

Existing passwords are gradually migrated to Argon2 on login.

Previously User used salted SHA512 with OpenLDAP-style prefix syntax and
Signup used crypt. Both models had their own hashing and verification
code. Now both use OpenLDAP-style syntax with support for all traditional
formats including crypt. Salted SHA512 is used for new User and Signup
passwords.

Existing Signup objects are migrated to the new format and remain functional.
User passwords now support gradual migration to another hash algorithm when
it is changed in the future.

This code is planned to be used for database-stored API and OAuth2 client
secrets.

Previously the getmails API endpoint did not match "receive_address" values
case-insensitivly like it did pre-v2. To solve this independent of database
collations, all existing mail receive addresses are converted to lower-case
and new/changed receive addresses are constraint to ASCII lower-case letters,
digits and symbols.