Function validate_confs 

fn validate_confs<T, U>(config_a: &T, config_b: &U) -> Result
where
    T: ConfigAuthorizedKeyEntries + ConfigSystemUserIds,
    U: ConfigAuthorizedKeyEntries + ConfigSystemUserIds,

Validates overlapping assumptions of two configuration objects.

Ensures that config_a and config_b have no overlapping system user IDs or SSH authorized_keys.

Errors

Returns an error if there are

• duplicate system users
• duplicate SSH authorized keys (by comparing the actual SSH public keys)