Function handle_credential 

pub fn handle_credential(
    cmd: CredentialCommand,
    repo_path: PathBuf,
    env_config: &EnvironmentConfig,
    passphrase_provider: Arc<dyn PassphraseProvider + Send + Sync>,
) -> Result<()>

Dispatch an auths credential … subcommand.

Args:

• cmd: The parsed credential command.
• repo_path: Resolved registry repository path.
• env_config: Environment configuration for context building.
• passphrase_provider: Passphrase source for issuer key access.

Usage:

handle_credential(cmd, repo_path, &env_config, passphrase_provider)?;