Login via StackExchange no longer works #66
Description
As announced here: https://meta.stackexchange.com/questions/381456/openid-endpoints-and-url-will-be-removed-on-november-1-2022
StackExchange stopped the OpenID provider service in November 2022. Since then, login via StackExchange in TBro no longer works. This affects, the public instance as well as all private instances. This can not easily be fixed. A whole new authentication method needs to be implemented. Also, porting user accounts to that new system will require a lot of manual effort. However, old carts are not lost as it is possible to extract their content from the database and re-import it into TBro.