### Bug Description Both SC7 and SC8 fail when attempting to interact with a store proxy using any of the currently supported subcommands. I’ve confirmed that the macaroon file generated by `export-login` is valid by successfully building an image from the proxy with `ubuntu-image`, so the issue (based on the logs below) seems to be with `candid` login functionality. ### To Reproduce ```sh export SNAPCRAFT_ADMIN_MACAROON="$(cat store-export-ce-team-test-20240107T001605.macaroon)" export SNAPCRAFT_STORE_AUTH=onprem export STORE_DASHBOARD_URL="https://store-proxy.lxd/publishergw" export STORE_UPLOAD_URL="https://store-proxy.lxd" snapcraft export-login store-proxy.creds export SNAPCRAFT_STORE_CREDENTIALS="$(cat store-proxy.creds)" snapcraft list-revisions core22 ``` ### Environment Snapcraft 7.5.4 (rev. 10085) & Snapcraft 8.0.1 (rev. 10279) Ubuntu 23.10 x86_64 6.2.16+ Kernel ### snapcraft.yaml ```shell N/A ``` ### Relevant log output ```shell 2024-01-18 16:16:17.787 Starting Snapcraft 7.5.4 2024-01-18 16:16:17.789 Storing credentials for 'snapcraft' on 'store-proxy.lxd' in keyring 'auth MemoryKeyring'. 2024-01-18 16:16:17.789 Retrieving credentials for 'snapcraft' on 'store-proxy.lxd' from keyring 'auth MemoryKeyring'. 2024-01-18 16:16:17.789 craft-store error: Credentials could not be parsed. Expected valid Candid credentials. 2024-01-18 16:16:17.789 Full execution log: '/home/jmbrock/.local/state/snapcraft/log/snapcraft-20240118-161617.786092.log' ``` ### Additional context _No response_