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docs/getting_started/authentication.md

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+# Authentication
+
+FastGPT API uses API keys for authentication. This guide covers how to securely manage and use your API keys with the SDK.
+
+## API Key Format
+
+FastGPT API keys typically start with `fastgpt-`:
+
+```
+fastgpt-xxxxxxxxxxxxxxxxxxxxxx
+```
+
+## Setting Your API Key
+
+### Method 1: Directly in Code (Not Recommended)
+
+```python
+from fastgpt_client import ChatClient
+
+client = ChatClient(api_key="fastgpt-xxxxx")
+```
+
+!!! warning
+    Never commit API keys to version control!
+
+### Method 2: Environment Variables (Recommended)
+
+Create a `.env` file:
+
+```bash
+API_KEY=fastgpt-xxxxx
+BASE_URL=http://localhost:3000
+```
+
+Use `python-dotenv` to load it:
+
+```python
+import os
+from dotenv import load_dotenv
+from fastgpt_client import ChatClient
+
+load_dotenv()
+
+client = ChatClient(
+    api_key=os.getenv("API_KEY"),
+    base_url=os.getenv("BASE_URL")
+)
+```
+
+Add `.env` to your `.gitignore`:
+
+```
+.env
+```
+
+### Method 3: System Environment Variables
+
+Set the environment variable in your shell:
+
+```bash
+# Linux/macOS
+export FASTGPT_API_KEY="fastgpt-xxxxx"
+export FASTGPT_BASE_URL="http://localhost:3000"
+
+# Windows (Command Prompt)
+set FASTGPT_API_KEY=fastgpt-xxxxx
+set FASTGPT_BASE_URL=http://localhost:3000
+
+# Windows (PowerShell)
+$env:FASTGPT_API_KEY="fastgpt-xxxxx"
+$env:FASTGPT_BASE_URL="http://localhost:3000"
+```
+
+Then use it in Python:
+
+```python
+import os
+from fastgpt_client import ChatClient
+
+client = ChatClient(
+    api_key=os.getenv("FASTGPT_API_KEY"),
+    base_url=os.getenv("FASTGPT_BASE_URL", "http://localhost:3000")
+)
+```
+
+## Base URL Configuration
+
+The default base URL is `http://localhost:3000`. If you're using a different FastGPT instance:
+
+```python
+client = ChatClient(
+    api_key="fastgpt-xxxxx",
+    base_url="https://your-fastgpt-instance.com"
+)
+```
+
+## Authentication Errors
+
+If authentication fails, the SDK raises an `AuthenticationError`:
+
+```python
+from fastgpt_client import ChatClient
+from fastgpt_client.exceptions import AuthenticationError
+
+try:
+    with ChatClient(api_key="invalid-key") as client:
+        response = client.create_chat_completion(
+            messages=[{"role": "user", "content": "Hello"}]
+        )
+except AuthenticationError as e:
+    print(f"Authentication failed: {e}")
+```
+
+## Security Best Practices
+
+1. **Never expose API keys** in client-side code (browsers, mobile apps)
+2. **Use environment variables** to store keys
+3. **Rotate keys regularly** for production applications
+4. **Use separate keys** for different environments (dev, staging, prod)
+5. **Monitor usage** to detect unauthorized access
+6. **Commit `.env` to `.gitignore`** to prevent accidental commits
+
+## Next Steps
+
+- [Quick Start](quick_start.md) - Start using the SDK
+- [Error Handling](../advanced/error_handling.md) - Learn to handle errors properly