When a registry token cannot be found, or a token is invalid, cargo displays an error recommending cargo login.

Starting in rust 1.67 with #10592, the message was amended to include the environment variable that could also be used to include the token.

error: no token found for `alternative`, please run `cargo login --registry alternative`
or use environment variable CARGO_REGISTRIES_ALTERNATIVE_TOKEN

With -Z credential-process, if cargo:token is not in registry.global-credential-providers or registries.<NAME>.credential-provider the suggested environment variable will not work.