[FEATURE] Add universal dependency support

It can often be useful to essentially add an app-wide dependency. Suppose, for example, you want to enforce http basic auth on non-production environments:

async def basic_auth(credentials: HTTPBasicCredentials = Depends(security)):
    if (settings.SITEWIDE_BASIC_AUTH and (
            credentials.username != settings.SITEWIDE_BASIC_AUTH_USERNAME or
            credentials.password != settings.SITEWIDE_BASIC_AUTH_PASSWORD)):
        raise HTTPException(
            status_code=HTTP_401_UNAUTHORIZED,
            detail="Incorrect email or password",
            headers={"WWW-Authenticate": "Basic"},
        )

app.add_dependency(basic_auth)

Now, you could do something similar with middleware, but then you’d miss out on dependency injection. You can already do something similar for included routers, but not for the entire app.

Just a thought.

[dmontagu]

You can achieve this for the full app now via:

1. app_router = APIRouter()
2. Add all desired routes to app_router
3. Call app.include_router(app_router, dependencies=app_dependencies)

Maybe you realized this already, just wanted to share in case it’s useful (I use this pattern myself).

---

In general, I agree that it would make more sense to me to specify dependencies when initializing the routers, rather than when including the routers, but due to the way that the route creation decorators work, and the way route inclusion works, I think it would be a relatively involved refactor to change this. I assume this is why @tiangolo designed the API the way it is now.

[dimaqq]

If I use .include_router(router, dependencies=Depends(security)) and then one of the endpoints needs to see the credentials that security decoded from the Authorization header field, how do I go about that?

1. is there a way to poke at router dependency values somehow?
2. should I explicitly include that dependency in the special endpoint?
   • will fastapi eval it once and cache the result?