feat: add session handling

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/identity/session.guard.ts

@@ -0,0 +1,49 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import {
+  CanActivate,
+  ExecutionContext,
+  Injectable,
+  UnauthorizedException,
+} from '@nestjs/common';
+
+import { NotInDBError } from '../errors/errors';
+import { ConsoleLoggerService } from '../logger/console-logger.service';
+import { User } from '../users/user.entity';
+import { UsersService } from '../users/users.service';
+
+@Injectable()
+export class SessionGuard implements CanActivate {
+  constructor(
+    private readonly logger: ConsoleLoggerService,
+    private userService: UsersService,
+  ) {
+    this.logger.setContext(SessionGuard.name);
+  }
+
+  async canActivate(context: ExecutionContext): Promise<boolean> {
+    const request: Request & { session?: { user: string }; user?: User } =
+      context.switchToHttp().getRequest();
+    if (!request.session) {
+      this.logger.debug('The user has no session.');
+      throw new UnauthorizedException("You're not logged in");
+    }
+    try {
+      request.user = await this.userService.getUserByUsername(
+        request.session.user,
+      );
+      return true;
+    } catch (e) {
+      if (e instanceof NotInDBError) {
+        this.logger.debug(
+          `The user '${request.session.user}' does not exist, but has a session.`,
+        );
+        throw new UnauthorizedException("You're not logged in");
+      }
+      throw e;
+    }
+  }
+}