feat: add local auth strategy

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

src/identity/local/local.strategy.ts

@@ -0,0 +1,44 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { Injectable, UnauthorizedException } from '@nestjs/common';
+import { AuthGuard, PassportStrategy } from '@nestjs/passport';
+import { Strategy } from 'passport-local';
+
+import { NotInDBError } from '../../errors/errors';
+import { UserRelationEnum } from '../../users/user-relation.enum';
+import { User } from '../../users/user.entity';
+import { UsersService } from '../../users/users.service';
+import { IdentityService } from '../identity.service';
+
+@Injectable()
+export class LocalAuthGuard extends AuthGuard('local') {}
+
+@Injectable()
+export class LocalStrategy extends PassportStrategy(Strategy, 'local') {
+  constructor(
+    private userService: UsersService,
+    private identityService: IdentityService,
+  ) {
+    super();
+  }
+
+  async validate(username: string, password: string): Promise<User> {
+    try {
+      const user = await this.userService.getUserByUsername(username, [
+        UserRelationEnum.IDENTITIES,
+      ]);
+      await this.identityService.loginWithLocalIdentity(user, password);
+      return user;
+    } catch (e) {
+      if (e instanceof NotInDBError) {
+        throw new UnauthorizedException(
+          'This username and password combination did not work.',
+        );
+      }
+      throw e;
+    }
+  }
+}