Returning a RedirectResponse in a dependency

[philmade]

Description

How can I return a Redirect in a dependency to be executed in a conditional? In the example below, the code works, but I just get an exception. I want a redirect.:

def logged_in(user: models.User = Depends(current_user)):
    if not user.is_authenticated:
        raise HTTPException(status_code=303, detail="You need to login")

@users.get('/channel/{username}', dependencies=[Depends(logged_in)])
def channel(*, username: str,
            request: Request,
            current_user: models.User = Depends(current_user),
            db: Session = Depends(get_db))
    do_something()

Below is what I want, but when I use this dependency nothing happens because doesn't use the return value. I can't think of a way to do this without referencing the Dependency directly.

def logged_in(user: models.User = Depends(current_user)):
    if not user.is_authenticated:
        return RedirectResponse(url='/login')

@users.get('/channel/{username}', dependencies=[Depends(logged_in)])
def channel(*, username: str,
             request: Request,
            current_user: models.User = Depends(current_user),
            db: Session = Depends(get_db))
    do_something()

This works, but I have to put it in every single endpoint:
@users.get('/channel/{username}', dependencies=[Depends(logged_in)])

def channel(*, username: str,
             request: Request,
            current_user: models.User = Depends(current_user),
            db: Session = Depends(get_db)):
     
     if not user.is_authenticated:
            return RedirectResponse(url='/login')

[philmade]

A guy on Gitter helped me with this. The trick is to not return the Redirect - just call it. Like this:

def logged_in(user: models.User = Depends(current_user)):
    if not user.is_authenticated:
        RedirectResponse(url='/login')

[phy25]

I doubt if this works at all. At least the following does not work for me.

from fastapi import FastAPI, Depends
from starlette.responses import RedirectResponse

app = FastAPI()

def redirect() -> bool:
    RedirectResponse(url='/login')
    return True

@app.get('/')
def index(should_redirect: bool = Depends(redirect)):
    return should_redirect

What I did before is to use custom exception handler:

from fastapi import FastAPI, Depends
from starlette.requests import Request
from starlette.responses import RedirectResponse, Response

app = FastAPI()

class RequiresLoginException(Exception):
    pass

async def redirect() -> bool:
    raise RequiresLoginException

@app.exception_handler(RequiresLoginException)
async def exception_handler(request: Request, exc: RequiresLoginException) -> Response:
    return RedirectResponse(url='/login')

@app.get('/')
async def index(should_redirect: bool = Depends(redirect)) -> bool:
    return should_redirect

[philmade]

Yeah you're correct - I had thought that it worked but it does not. Without specifically referencing the dependency in the endpoint, I can't easily get a redirect to happen at the dependency level, it only will happen at the endpoint level.

Anyone got an idea on how to force a redirect?

[phy25]

@NomeChomsky does my exception-based solution work for you?

[philmade]

Hey I just tried that. It does work. I didn't fully understand it - so the Exception is somehow allowing a return statement to be triggered, but an actual return statement won't get triggered?

Its a good workaround. Would be good to be able to return / exectute a Redirect without a custom exception.

thank you for your help!

:)

[tiangolo]

Thanks for the help here @phy25 ! 🍰 👏

@NomeChomsky yeah, just what @phy25 said ☝️

[github-actions]

Assuming the original issue was solved, it will be automatically closed now. But feel free to add more comments or create new issues.

[bsatts]

Is there a way to define exception handlers on routers? There's currently no way to @router.exception_handler

[tiangolo]

Yeah, that's currently not supported @bsatts, only in the main app.

[eddyizm]

@NomeChomsky how did you implement that example to your user authentication? I am having the same issue but not sure how that got sorted out.

[fboerman]

@NomeChomsky @eddyizm I would also like to know how I can implement this. I want my dependency to trigger a redirect when it cant find a certain cookie. I cant find in the docs a proper way to implement this without also thouching the main app source code.

@phy25 solution is therefor not possible for me

[gavrilovne]

@NomeChomsky @eddyizm I would also like to know how I can implement this. I want my dependency to trigger a redirect when it cant find a certain cookie. I cant find in the docs a proper way to implement this without also thouching the main app source code.

@phy25 solution is therefor not possible for me

Hi!
Try it

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token", auto_error=False)


async def check_auth(token: str = Depends(oauth2_scheme)):
    if not token:
        raise HTTPException(
            status_code=status.HTTP_307_TEMPORARY_REDIRECT,
            headers={'Location': '/login'})
    return True


@router.get("/login")
async def login(request: Request):
    return auth_template.TemplateResponse("login.html", {"request": request})


@router.get("/test")
async def test(auth: bool = Depends(check_auth)):
    return "OK"

[fboerman]

@NomeChomsky @eddyizm I would also like to know how I can implement this. I want my dependency to trigger a redirect when it cant find a certain cookie. I cant find in the docs a proper way to implement this without also thouching the main app source code.
@phy25 solution is therefor not possible for me

Hi! Try it

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token", auto_error=False)


async def check_auth(token: str = Depends(oauth2_scheme)):
    if not token:
        raise HTTPException(
            status_code=status.HTTP_307_TEMPORARY_REDIRECT,
            headers={'Location': '/login'})
    return True


@router.get("/login")
async def login(request: Request):
    return auth_template.TemplateResponse("login.html", {"request": request})


@router.get("/test")
async def test(auth: bool = Depends(check_auth)):
    return "OK"

thanks @gavrilovne ! Thanks works perfectly!