Add auth to FastAPI via Middleware and include in OpenAPI

Question

Basic goal: A means of authenticating most (but not all) routes in one place (a separate file), seamlessly so that I don't have to add code/documentation to every one of the routes in order to get auth or openapi to work.

I would like to implement a basic Bearer Authorization in FastAPI, but do so in class-based middleware. I've done this successfully, but I have not seen how to do this in a way that OpenAPI is aware of it (i.e., there's no way to set auth tokens in the docs).

class AuthMiddleware:
    def __init__(self, settings):
        self.settings = settings

    async def __call__(self, request: Request, call_next):
        if self.is_protected_url(request.method, request.url.path):
            auth = request.headers.get("Authorization")
            scheme, data = (auth or " ").split(" ", 1)
            if scheme != "Bearer":
                return JSONResponse(None, 401, {"WWW-Authenticate": "Bearer"})
            if data != self.settings.auth_token:
                return JSONResponse(None, 401, {"WWW-Authenticate": "Bearer"})

        return await call_next(request)

    def is_protected_url(self, method, url):
        """ does what it does """

In the main file:

from path.to.auth import AuthMiddleware

auth_middleware = AuthMiddleware(settings)
app.middleware("http")(auth_middleware)

There seems to be some existing auth classes to use, but I can't figure out how to properly get them to work in a class-based Middleware that is in a separate file (Depends doesn't resolve).

See

Have two APIRouters on the root level - one for authenticated routes and one for those without. Import OAuth2PasswordBearer - from fastapi.security import OAuth2PasswordBearer, and add it as a default dependency to the API router that handles your routes that require authentication. Add any routes (or other routers) under that specific router. FastAPI's built-in openapi generator will know about this class and add the proper information (and send authentication) when you use that class. See fastapi.tiangolo.com/tutorial/security/simple-oauth2/… — MatsLindh
– MatsLindh, Commented Dec 16, 2024 at 22:40

carpe171 · Accepted Answer · 2025-05-02 23:14:11Z

You can use a global dependency: https://fastapi.tiangolo.com/tutorial/dependencies/global-dependencies/

from fastapi import Depends, FastAPI, Request
from fastapi.openapi.utils import get_openapi

async def verify_token(request: Request):
    # verify token code
    pass

app = FastAPI(
    title="<title>",
    description="<desc>",
    version="<version>",
    dependencies=[Depends(verify_token)]
)

def custom_openapi():
    if app.openapi_schema:
        return app.openapi_schema
    openapi_schema = get_openapi(
        title="<title>",
        description="<desc>",
        version="<version>",
        routes=app.routes,
    )
    openapi_schema["components"]["securitySchemes"] = {
        "BearerAuth": {
            "type": "http",
            "scheme": "bearer",
            "bearerFormat": "sso-jwt",
        }
    }
    openapi_schema["security"] = [{"BearerAuth": []}]
    app.openapi_schema = openapi_schema
    return app.openapi_schema

app.openapi = custom_openapi

Make sure to configure bearerFormat for your usage.

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