# How to Customize your Authentication Flow?
## 1. Enable Custom Auth in Settings
* Go to the **right-hand sidebar → Settings → Configuration**.
* Under **Custom Auth**, toggle **Enable Custom Authentication**.
* Save your changes.
## 2. Open the Custom Auth Flow
* Navigate to the **fastnCustomAuth** flow.
* This flow always begins with an **On API Request** trigger.
## 3. Initialize Flow Variables
* Add variables such as `baseURL` and `APIKey`.
* These can be predefined defaults for your flow, but you can alter them if needed.
## 4. Apply Token Validation (Switch Step)
* At this stage, the flow checks the Authorization header against the predefined Fastn secret (`fastn_mcp_client_api_key`).
* **Condition 1:** If `headers.authorization` **equals**
```
Bearer {{secrets.fastn_mcp_client_api_key}}
```
→ **Pass**.
* **Condition 2:** If `headers.authorization` **equals**
```
{{secrets.fastn_mcp_client_api_key}}
```
→ **Pass**.
**When one of the conditions matches:**
* The flow returns a **user object** that contains:
* `tenantId`
* `role`
* `expiresIn`
* All inside a success response.
**When no conditions match:**
* The flow continues to the **Logger** step for tracking request headers.
## 5. Handle Logs and External Checks
* **Logger Step** → capture the request headers.
* **GET Request (HTTP API)** → check if the user exists externally.
* **Final Switch Step**
* If user exists → return user details.
* If not → return error and unauthorized.
## 6. Save and Customize
* Save the flow once configured.
* You can customize the logic to match your own authentication provider, add extra validation rules, or enrich the returned user object.
> With this setup, you decide exactly how requests are authenticated and what user details are returned.
