docs: add telegram oauth guide

docs/features/telegram-oauth.md

@@ -0,0 +1,55 @@
+---
+sidebar_position: 3
+title: Telegram OAuth
+---
+
+<div style={{ display: 'flex', justifyContent: 'center' }}>
+  <img src="/features/tg-login/tg-login-preview.webp" alt="Telegram OAuth" width="800" style={{ borderRadius: '8px' }} />
+</div>
+
+---
+
+Telegram OAuth is a feature that allows you to authenticate to Remnawave dashboard using Telegram.
+
+### .env configuration
+
+```bash title="Editing .env file"
+cd ~/opt/remnawave && nano .env
+```
+
+```bash title=".env configuration"
+# Your Telegram bot token, you can get it from @BotFather
+# If it already defined in .env, you can skip this step
+TELEGRAM_BOT_TOKEN="1234567890:ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+# Enable Telegram OAuth
+TELEGRAM_OAUTH_ENABLED=true
+
+# List of admin IDs (numbers, not strings), separated by commas
+TELEGRAM_OAUTH_ADMIN_IDS=[1234567890, 1234567891]
+```
+
+`TELEGRAM_OAUTH_ADMIN_IDS` - manages the list of admins who can access the Remnawave dashboard.
+
+### How to get Telegram bot token
+
+1. Go to [@BotFather](https://t.me/BotFather)
+2. Create a new bot and get the token
+3. Set the token in the `.env` file
+
+### Setting up the bot
+
+:::danger
+It is necessary to set the domain under which you log in to the Remnawave dashboard.
+:::
+
+1. Go to [@BotFather](https://t.me/BotFather)
+2. Send command `/mybots` and select previous created bot
+3. Select option `Bot settings` → `Domain`
+4. Select option `Set domain`
+
+Now you need to send a message containing domain under which you log in to the Remnawave dashboard.
+
+```bash
+https://panel.domain.com
+```