refactor(server): auth (#5895)

Remove `next-auth` and implement our own Authorization/Authentication system from scratch.

## Server

- [x] tokens
  - [x] function
  - [x] encryption

- [x] AuthController
  - [x] /api/auth/sign-in
  - [x] /api/auth/sign-out
  - [x] /api/auth/session
  - [x] /api/auth/session (WE SUPPORT MULTI-ACCOUNT!)

- [x] OAuthPlugin
  - [x] OAuthController
  - [x] /oauth/login
  - [x] /oauth/callback
  - [x] Providers
    - [x] Google
    - [x] GitHub

## Client

- [x] useSession
- [x] cloudSignIn
- [x] cloudSignOut

## NOTE:

Tests will be adding in the future

packages/backend/server/src/plugins/oauth/service.ts

@@ -0,0 +1,39 @@
+import { randomUUID } from 'node:crypto';
+
+import { Injectable } from '@nestjs/common';
+
+import { SessionCache } from '../../fundamentals';
+import { OAuthProviderFactory } from './register';
+import { OAuthProviderName } from './types';
+
+const OAUTH_STATE_KEY = 'OAUTH_STATE';
+
+interface OAuthState {
+  redirectUri: string;
+  provider: OAuthProviderName;
+}
+
+@Injectable()
+export class OAuthService {
+  constructor(
+    private readonly providerFactory: OAuthProviderFactory,
+    private readonly cache: SessionCache
+  ) {}
+
+  async saveOAuthState(state: OAuthState) {
+    const token = randomUUID();
+    await this.cache.set(`${OAUTH_STATE_KEY}:${token}`, state, {
+      ttl: 3600 * 3 * 1000 /* 3 hours */,
+    });
+
+    return token;
+  }
+
+  async getOAuthState(token: string) {
+    return this.cache.get<OAuthState>(`${OAUTH_STATE_KEY}:${token}`);
+  }
+
+  availableOAuthProviders() {
+    return this.providerFactory.providers;
+  }
+}