[Generic] Using OAUTH2_AUTHORIZE_URL results in incorrect authorize URL

[westernspion]

Bug description

Using OAUTH2_AUTHORIZE_URL seems to improperly construct the authorize URL used in the login process. It seems to prepend the base URL (in my case, localhost:8000/hub/) to the actual authorize URL, resulting in a 404 not found.

When setting directly through Jupyter config file, as
c.GenericOAuthenticator.authorize_url = "https://acme.okta.com/oauth2/<redacted>/v1/authorize?scope=openid email
it works as expected and I am redirected to my Okta OAuth provider as expected.

Expected behaviour

Using OAUTH2_AUTHORIZE_URL should not concatenate the base URL to the authorize endpoint. It should behave the same way as the Jupyterhub c.GenericOAuthenticator.authorize_url parameter

Example

When set with OAUTH2_AUTHORIZE_URL environment variable, after clicking the sign in with my provider link from Jupyterhub I get directed to this URL, which results in a 404 with Jupyterhub since this URL doesn't exist
http://localhost:8000/hub/%22https://acme.okta.com/oauth2/<redacted>/v1/authorize?scop.....
^ Removing the base url manually completes the sign in process

But when I use the parameter through Jupyterhubs config it works as expected
https://acme.okta.com/oauth2/<redacted>/v1/authorize?scop.....

Setup
Python 3.8.13
jupyterhub 2.3.1
jupyterlab 3.4.4
amazonlinux:2 container

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