GitLab as an OAuth2 provider for Python or fastAPI

import os
import time
import requests as rest_client
from urllib.parse import urljoin
from fastapi import APIRouter
from starlette.responses import RedirectResponse
from starlette.exceptions import HTTPException
from starlette.requests import Request
from starlette.status import (
    HTTP_400_BAD_REQUEST
)

GITLAB_BASE_DOMAIN = 'https://git.youdomain.com'
APP_ID = os.environ.get("APP_ID", None)
APP_SECRET = os.environ.get("APP_SECRET", None)
REDIRECT_URI = os.environ.get("REDIRECT_URI", None)

router = APIRouter()


@router.get("/users/login", tags=["authentication"])
async def login():
    unique_state_hash = int(round(time.time() * 1000))
    url = f"{GITLAB_BASE_DOMAIN}/oauth/authorize?client_id={APP_ID}&redirect_uri={REDIRECT_URI}&response_type=code&state={unique_state_hash}"
    return RedirectResponse(
        url=url)


@router.get("/oauth2/callback/gitlab", tags=["authentication"])
async def callback_gitlab(request: Request):
    code = request.query_params.get("code", None)
    res = rest_client.post(f"{GITLAB_BASE_DOMAIN}/oauth/token", data={'client_id': APP_ID,
                                                                      'client_secret': APP_SECRET,
                                                                      'code': code,
                                                                      'grant_type': 'authorization_code',
                                                                      'redirect_uri': REDIRECT_URI})
    json_res = res.json()
    access_token = "access_token"
    if access_token not in json_res:
        raise HTTPException(
            status_code=HTTP_400_BAD_REQUEST,
            detail=f"GitLab OAuth2 failure"
        )
    user_info_request = urljoin(GITLAB_BASE_DOMAIN, f"/api/v4/user?access_token={json_res.get(access_token,'')}")
    user_res = rest_client.get(user_info_request)
    user_res_data = user_res.json()
    print(user_res_data)
    return user_res_data