Env URL and basePath redundant Warning

[wintangz]

Hello, I am upgrading from V4 to V5 and faced this warning:
[auth][warn][env-url-basepath-redundant].

I read the doc (https://authjs.dev/reference/warnings/#env-url-basepath-redundant) and it says that

"AUTH_URL (or NEXTAUTH_URL) and authConfig.basePath are both declared. This is a configuration mistake - you should either remove the authConfig.basePath configuration, or remove the pathname of AUTH_URL (or NEXTAUTH_URL). Only one of them is needed."

However, I have no idea what is the "authConfig.basePath" and can't find it anywhere. I tried removing the AUTH_URL in my .env but this cause the error UnknownAction when I try to sign in.
I am not sure what the problem is. It would be greatly appreciated if someone could help.

[rsippl]

I can confirm this. I need to set AUTH_URL (being behind a reverse proxy), and although I never set basePath in my auth config, I keep getting that warning. I bet this is a bug, the check for basePath (in case AUTH_URL is set, probably here) is likely done after basePath is set to some default value.
Other than filling the logs with garbage, this probably does no harm.

[fabpico]

I opened an issue for this: #11522

[k-taro56]

We fixed this in #11636.