FastAPI集成Authlib实现Google OAuth时遇URL转bytes类型错误

问题场景 #

使用Authlib和FastAPI实现Google OAuth登录功能，严格遵循Authlib官方FastAPI示例开发，仅替换了Google的client_id和client_secret，未修改其他代码，但调用登录接口时触发如下错误：

ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/uvicorn/protocols/http/httptools_impl.py", line 436, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/uvicorn/middleware/proxy_headers.py", line 78, in __call__
    return await self.app(scope, receive, send)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/fastapi/applications.py", line 276, in __call__
    await super().__call__(scope, receive, send)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/applications.py", line 122, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/middleware/sessions.py", line 86, in __call__
    await self.app(scope, receive, send_wrapper)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 79, in __call__
    raise exc
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/fastapi/middleware/asyncexitstack.py", line 21, in __call__
    raise e
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/fastapi/middleware/asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/routing.py", line 718, in __call__
    await route.handle(scope, receive, send)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/starlette/routing.py", line 66, in app
    response = await func(request)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/fastapi/routing.py", line 237, in app
    raw_response = await run_endpoint_function(
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/fastapi/routing.py", line 163, in run_endpoint_function
    return await dependant.call(**values)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/main.py", line 41, in login
    return await oauth.google.authorize_redirect(request, redirect_uri)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/integrations/starlette_client/apps.py", line 29, in authorize_redirect
    rv = await self.create_authorization_url(redirect_uri, **kwargs)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/integrations/base_client/async_app.py", line 105, in create_authorization_url
    return self._create_oauth2_authorization_url(
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/integrations/base_client/sync_app.py", line 265, in _create_oauth2_authorization_url
    url, state = client.create_authorization_url(
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/oauth2/client.py", line 155, in create_authorization_url
    uri = prepare_grant_uri(
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/oauth2/rfc6749/parameters.py", line 66, in prepare_grant_uri
    return add_params_to_uri(uri, params)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/common/urls.py", line 99, in add_params_to_uri
    query = add_params_to_qs(query, params)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/common/urls.py", line 90, in add_params_to_qs
    return url_encode(qs)
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/common/urls.py", line 28, in url_encode
    encoded.append((to_bytes(k), to_bytes(v)))
  File "/Users/alvartabe/Desktop/FastAPI-GoogleOAuth/venv/lib/python3.10/site-packages/authlib/common/encoding.py", line 15, in to_bytes
    return bytes(x)
TypeError: cannot convert 'URL' object to bytes

错误原因 #

报错核心是Authlib版本与Starlette/FastAPI的URL对象兼容性问题：旧版Authlib的URL编码逻辑无法直接处理Starlette生成的URL对象（比如通过request.url_for()返回的结果），尝试将其转为bytes时触发类型错误。

修复方案 #

将传入authorize_redirect的redirect_uri从URL对象转为字符串即可：

1. 找到登录接口中生成redirect_uri的代码，原代码可能为：

redirect_uri = request.url_for('auth')
return await oauth.google.authorize_redirect(request, redirect_uri)

2. 修改为将URL对象转为字符串：

redirect_uri = str(request.url_for('auth'))
return await oauth.google.authorize_redirect(request, redirect_uri)

验证 #

修改后重新启动FastAPI服务，访问登录接口即可正常跳转到Google授权页面，错误不再出现。

内容的提问来源于stack exchange，提问作者Alvaro Artavia