snapcast-server 0.6.0

//! Streaming client authentication.
//!
//! Implement [`AuthValidator`] for custom authentication (database, LDAP, etc.)
//! or use [`StaticAuthValidator`] for config-file-based users/roles.

use std::collections::HashMap;
use std::sync::Arc;

use subtle::ConstantTimeEq;

/// Constant-time byte comparison to prevent timing attacks.
fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
    a.ct_eq(b).into()
}

/// Result of successful authentication.
#[derive(Debug, Clone)]
pub struct AuthResult {
    /// Authenticated username.
    pub username: String,
    /// Granted permissions (e.g. "Streaming", "Control").
    pub permissions: Vec<String>,
}

/// Authentication error.
#[derive(Debug, Clone)]
pub enum AuthError {
    /// 401 — invalid or missing credentials.
    Unauthorized(String),
    /// 403 — authenticated but lacking required permission.
    Forbidden(String),
}

impl std::fmt::Display for AuthError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Unauthorized(msg) => write!(f, "Unauthorized: {msg}"),
            Self::Forbidden(msg) => write!(f, "Forbidden: {msg}"),
        }
    }
}

impl std::error::Error for AuthError {}

impl AuthError {
    /// HTTP-style error code.
    pub fn code(&self) -> i32 {
        match self {
            Self::Unauthorized(_) => 401,
            Self::Forbidden(_) => 403,
        }
    }

    /// Error message.
    pub fn message(&self) -> &str {
        match self {
            Self::Unauthorized(msg) | Self::Forbidden(msg) => msg,
        }
    }
}

/// Trait for validating streaming client credentials.
///
/// The server calls [`validate`](AuthValidator::validate) after receiving a Hello message.
/// Return [`AuthResult`] on success or [`AuthError`] on failure.
///
/// # Example: Custom validator
///
/// ```
/// use snapcast_server::auth::{AuthValidator, AuthResult, AuthError};
///
/// struct MyValidator;
///
/// impl AuthValidator for MyValidator {
///     fn validate(&self, scheme: &str, param: &str) -> Result<AuthResult, AuthError> {
///         // Look up in database, LDAP, etc.
///         Ok(AuthResult {
///             username: "user".into(),
///             permissions: vec!["Streaming".into()],
///         })
///     }
/// }
/// ```
/// Trait for validating streaming client credentials.
pub trait AuthValidator: Send + Sync {
    /// Validate credentials from the Hello message's auth field.
    fn validate(&self, scheme: &str, param: &str) -> Result<AuthResult, AuthError>;
}

/// Permission required for streaming clients.
pub const PERM_STREAMING: &str = "Streaming";

/// A role with named permissions.
#[derive(Debug, Clone)]
pub struct Role {
    /// Role name.
    pub name: String,
    /// Granted permissions.
    pub permissions: Vec<String>,
}

/// A user with credentials and role assignment.
#[derive(Debug, Clone)]
pub struct User {
    /// Username.
    pub name: String,
    /// Password (plaintext — hashing is the deployer's responsibility).
    pub password: String,
    /// Role name.
    pub role: String,
}

/// Config-file-based authentication matching the C++ implementation.
///
/// Validates Basic auth (`base64(user:password)`) against a static user/role list.
#[derive(Debug, Clone)]
pub struct StaticAuthValidator {
    users: HashMap<String, (String, Arc<Role>)>, // name → (password, role)
}

impl StaticAuthValidator {
    /// Create from user and role lists.
    pub fn new(users: Vec<User>, roles: Vec<Role>) -> Self {
        let role_map: HashMap<String, Arc<Role>> = roles
            .into_iter()
            .map(|r| (r.name.clone(), Arc::new(r)))
            .collect();
        let empty_role = Arc::new(Role {
            name: String::new(),
            permissions: vec![],
        });
        let user_map = users
            .into_iter()
            .map(|u| {
                let role = role_map
                    .get(&u.role)
                    .cloned()
                    .unwrap_or_else(|| empty_role.clone());
                (u.name, (u.password, role))
            })
            .collect();
        Self { users: user_map }
    }
}

impl AuthValidator for StaticAuthValidator {
    fn validate(&self, scheme: &str, param: &str) -> Result<AuthResult, AuthError> {
        if !scheme.eq_ignore_ascii_case("basic") {
            return Err(AuthError::Unauthorized(format!(
                "Unsupported auth scheme: {scheme}"
            )));
        }

        // Decode base64(user:password)
        use base64::Engine;
        let decoded = base64::engine::general_purpose::STANDARD
            .decode(param)
            .map_err(|_| AuthError::Unauthorized("Invalid base64".into()))?;
        let decoded = String::from_utf8(decoded)
            .map_err(|_| AuthError::Unauthorized("Invalid UTF-8".into()))?;
        let (username, password) = decoded
            .split_once(':')
            .ok_or_else(|| AuthError::Unauthorized("Expected user:password".into()))?;

        let (stored_pw, role) = self
            .users
            .get(username)
            .ok_or_else(|| AuthError::Unauthorized("Unknown user".into()))?;

        if !constant_time_eq(stored_pw.as_bytes(), password.as_bytes()) {
            return Err(AuthError::Unauthorized("Wrong password".into()));
        }

        Ok(AuthResult {
            username: username.to_string(),
            permissions: role.permissions.clone(),
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn test_validator() -> StaticAuthValidator {
        StaticAuthValidator::new(
            vec![
                User {
                    name: "admin".into(),
                    password: "secret".into(),
                    role: "full".into(),
                },
                User {
                    name: "player".into(),
                    password: "play".into(),
                    role: "streaming".into(),
                },
            ],
            vec![
                Role {
                    name: "full".into(),
                    permissions: vec!["Streaming".into(), "Control".into()],
                },
                Role {
                    name: "streaming".into(),
                    permissions: vec!["Streaming".into()],
                },
            ],
        )
    }

    fn basic(user: &str, pass: &str) -> String {
        use base64::Engine;
        base64::engine::general_purpose::STANDARD.encode(format!("{user}:{pass}"))
    }

    #[test]
    fn valid_credentials() {
        let v = test_validator();
        let result = v.validate("Basic", &basic("admin", "secret")).unwrap();
        assert_eq!(result.username, "admin");
        assert!(result.permissions.contains(&"Streaming".into()));
        assert!(result.permissions.contains(&"Control".into()));
    }

    #[test]
    fn wrong_password() {
        let v = test_validator();
        let err = v.validate("Basic", &basic("admin", "wrong")).unwrap_err();
        assert_eq!(err.code(), 401);
    }

    #[test]
    fn unknown_user() {
        let v = test_validator();
        let err = v.validate("Basic", &basic("nobody", "x")).unwrap_err();
        assert_eq!(err.code(), 401);
    }

    #[test]
    fn unsupported_scheme() {
        let v = test_validator();
        let err = v.validate("Bearer", "token123").unwrap_err();
        assert_eq!(err.code(), 401);
    }

    #[test]
    fn streaming_only_user() {
        let v = test_validator();
        let result = v.validate("Basic", &basic("player", "play")).unwrap();
        assert_eq!(result.username, "player");
        assert!(result.permissions.contains(&"Streaming".into()));
        assert!(!result.permissions.contains(&"Control".into()));
    }
}