FastAPI async def function not asking credentials even though it is expected to for a post method

Question

I have a FastAPI app which serves some documentation. I want to implement basic authentication with username and password for those endpoints.

security_service.py:

class SecurityService:
    security = HTTPBearer()

    @staticmethod
    def get_current_username(credentials: HTTPBasicCredentials = Depends(security)):
        username = credentials.username
        password = credentials.password
        if username == config.CREDENTIALS['USERNAME'] and password == config.CREDENTIALS['PASSWORD']:
            return username
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED
        )

app.py:

app.add_route(
    Template(doc_updater.document_path).substitute(
        group=group_name,
        service=service_name,
        endpoint=endpoint,
    ),
    doc_updater.document_endpoint,
    include_in_schema=False,
    methods=["POST"],
)

document_manager.py:

class DocumentManager:
    @classmethod
    async def document_endpoint(
            cls,
            request: Request,
            username: str = Depends(SecurityService.get_current_username)
    ) -> HTMLResponse:
        # Return the markdown documentation as json.

However, when I hit the endpoint which serves the documentation, it is working fine. Where as it should be asking me to enter username and password using a popup.