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# JWT
JSON Web Token (JWT) is an internet standard for creating access tokens based on JSON.
## Configuration
```py
from fastapi_users.authentication import JWTAuthentication
SECRET = "SECRET"
jwt_authentication = JWTAuthentication(secret=SECRET, lifetime_seconds=3600, tokenUrl="auth/jwt/login")
```
As you can see, instantiation is quite simple. It accepts the following arguments:
* `secret` (`Union[str, pydantic.SecretStr]`): A constant secret which is used to encode the token. **Use a strong passphrase and keep it secure.**
* `lifetime_seconds` (`int`): The lifetime of the token in seconds.
* `tokenUrl` (`Optional[str]`): The exact path of your login endpoint. It'll allow the interactive documentation to automatically discover it and get a working *Authorize* button. In most cases, you'll probably need a **relative** path, not absolute. You can read more details about this in the [FastAPI documentation](https://fastapi.tiangolo.com/tutorial/security/first-steps/#fastapis-oauth2passwordbearer). Defaults to `auth/jwt/login`.
* `name` (`Optional[str]`): Name of the backend. It's useful in the case you wish to have several backends of the same class. Each backend should have a unique name. Defaults to `jwt`.
```py
jwt_authentication = JWTAuthentication(
secret=SECRET,
lifetime_seconds=3600,
name="my-jwt",
)
```
## Login
This method will return a JWT token upon successful login:
!!! success "`200 OK`"
```json
{
"access_token": "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjoiOTIyMWZmYzktNjQwZi00MzcyLTg2ZDMtY2U2NDJjYmE1NjAzIiwiYXVkIjoiZmFzdGFwaS11c2VyczphdXRoIiwiZXhwIjoxNTcxNTA0MTkzfQ.M10bjOe45I5Ncu_uXvOmVV8QxnL-nZfcH96U90JaocI",
"token_type": "bearer"
}
```
> Check documentation about [login route](../../usage/routes.md#post-loginname).
## Logout
This backend does not provide a logout method (a JWT is valid until it expires).
## Authentication
This method expects that you provide a `Bearer` authentication with a valid JWT.
```bash
curl http://localhost:9000/protected-route -H'Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjoiOTIyMWZmYzktNjQwZi00MzcyLTg2ZDMtY2U2NDJjYmE1NjAzIiwiYXVkIjoiZmFzdGFwaS11c2VyczphdXRoIiwiZXhwIjoxNTcxNTA0MTkzfQ.M10bjOe45I5Ncu_uXvOmVV8QxnL-nZfcH96U90JaocI'
```
## Tip: Refresh
The default implementation **does not** provide a mechanism to refresh the JWT. However, you can implement it quite easily like this:
```py
from fastapi import Depends, Response
@router.post("/auth/jwt/refresh")
async def refresh_jwt(response: Response, user=Depends(fastapi_users.current_user(active=True))):
return await jwt_authentication.get_login_response(user, response)
```