[PLUGIN][OAuth2] Start adding OAuth2 support with client registration

This hardcodes the user, and has some other issues, so it is not yet
complete.

We follow mastodon's spec for automatic client registration, available
at both `/api/v1/apps` and a more reasonable `/oauth/client`. This
accepts a JSON POST with the client info and returns JSON with a
`client_id` and a `client_secret`, to be used with `/oauth/authorize`
and `/oauth/token`. It also, seemingly, requires returning an `id`
with unclear purpose.

The `/oauth/token` endpoint doesn't currently return a `me` field.

plugins/OAuth2/Entity/AuthCode.php

@@ -0,0 +1,152 @@
+<?php
+
+declare(strict_types = 1);
+
+// {{{ License
+// This file is part of GNU social - https://www.gnu.org/software/social
+//
+// GNU social is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GNU social is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with GNU social.  If not, see <http://www.gnu.org/licenses/>.
+// }}}
+
+/**
+ * OAuth2 Client
+ *
+ * @package   GNUsocial
+ *
+ * @author    Hugo Sales <hugo@hsal.es>
+ * @copyright 2022 Free Software Foundation, Inc http://www.fsf.org
+ * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
+ */
+
+namespace Plugin\OAuth2\Entity;
+
+use DateTimeInterface;
+use League\OAuth2\Server\Entities\AuthCodeEntityInterface;
+use Plugin\OAuth2\Repository;
+
+class AuthCode extends Token implements AuthCodeEntityInterface
+{
+    // {{{ Autocode
+    // @codeCoverageIgnoreStart
+    private string $id;
+    private DateTimeInterface $expiry;
+    private ?int $user_id = null;
+    private string $client_id;
+    private string $token_scopes;
+    private bool $revoked;
+    private DateTimeInterface $created;
+
+    public function setId(string $id): self
+    {
+        $this->id = mb_substr($id, 0, 64);
+        return $this;
+    }
+
+    public function getId(): string
+    {
+        return $this->id;
+    }
+
+    public function setExpiry(DateTimeInterface $expiry): self
+    {
+        $this->expiry = $expiry;
+        return $this;
+    }
+
+    public function getExpiry(): DateTimeInterface
+    {
+        return $this->expiry;
+    }
+
+    public function setUserId(?int $user_id): self
+    {
+        $this->user_id = $user_id;
+        return $this;
+    }
+
+    public function getUserId(): ?int
+    {
+        return $this->user_id;
+    }
+
+    public function setClientId(string $client_id): self
+    {
+        $this->client_id = mb_substr($client_id, 0, 64);
+        return $this;
+    }
+
+    public function getClientId(): string
+    {
+        return $this->client_id;
+    }
+
+    public function setTokenScopes(string $token_scopes): self
+    {
+        $this->token_scopes = $token_scopes;
+        return $this;
+    }
+
+    public function getTokenScopes(): string
+    {
+        return $this->token_scopes;
+    }
+
+    public function setRevoked(bool $revoked): self
+    {
+        $this->revoked = $revoked;
+        return $this;
+    }
+
+    public function getRevoked(): bool
+    {
+        return $this->revoked;
+    }
+
+    public function setCreated(DateTimeInterface $created): self
+    {
+        $this->created = $created;
+        return $this;
+    }
+
+    public function getCreated(): DateTimeInterface
+    {
+        return $this->created;
+    }
+
+    // @codeCoverageIgnoreEnd
+    // }}} Autocode
+
+    /**
+     * @return null|string
+     */
+    public function getRedirectUri()
+    {
+        return (new Repository\Client)->getClientEntity($this->getClientId())->getRedirectUri();
+    }
+
+    /**
+     * @param string $uri
+     */
+    public function setRedirectUri($uri)
+    {
+        /** @var Client $client */
+        $client = (new Repository\Client)->getClientEntity($this->getClientId());
+        $client->setRedirectUris($uri);
+    }
+
+    public static function schemaDef(): array
+    {
+        return parent::tokenSchema('oauth2_auth_code');
+    }
+}