pub fn validate_public_key(public_key: &str) -> Result<(), String> {
    if !public_key.starts_with('@') {
        return Err("Expected '@' sigil as first character".to_string());
    }

    let dot_index = match public_key.rfind('.') {
        Some(index) => index,
        None => return Err("could not find '.' character".to_string()),
    };

    if !&public_key.ends_with(".ed25519") {
        return Err("hashing algorithm must be ed25519".to_string());
    }

    let base64_str = &public_key[1..dot_index];

    if base64_str.len() != 44 {
        return Err("base64 data length is incorrect".to_string());
    }

    Ok(())
}