OAuth exception is swallowed and overwritten on login

[thekaveman]

The issue presents here: https://github.com/cal-itp/benefits/blob/main/benefits/oauth/views.py#L77

if result and result.status_code >= 400:
    exception = Exception(f"authorize_redirect error response [{result.status_code}]: {result.content.decode()}")
elif result is None:
    exception = Exception("authorize_redirect returned None")

The elif condition only checks result but does not look at exception.

The problem is, the previous line may have already caught and set exception: https://github.com/cal-itp/benefits/blob/main/benefits/oauth/views.py#L73

try:
    result = oauth_client.authorize_redirect(request, redirect_uri)
except Exception as ex:
    exception = ex

Thus, that original exception would be overwritten by exception = Exception("authorize_redirect returned None") which isn't necessarily true.

To Reproduce

Steps to reproduce the behavior:

1. Misconfigure a ClaimsProvider with bad scheme etc.
2. Place debug points on the above lines
3. Attempt login
4. See error

Expected behavior

The original exception is not overwritten and is the one that gets bubbled further.