qssh 0.4.3

//! GSSAPI/Kerberos Authentication Support
//!
//! **WARNING: This module contains placeholder implementations and is NOT functional.**
//! GSSAPI authentication is not yet implemented in QSSH.
//!
//! To enable enterprise Kerberos authentication, this module needs to be implemented
//! using a proper GSSAPI library such as `gssapi` or `libgssapi` crates.
//!
//! All public functions will return `QsshError::Protocol` with a clear error message
//! indicating that GSSAPI is not available.

use std::collections::HashMap;
use std::time::{SystemTime};
use crate::{Result, QsshError};

/// Error message for unimplemented GSSAPI functionality
const GSSAPI_NOT_IMPLEMENTED: &str = "GSSAPI authentication is not implemented. \
    Use public key or password authentication instead.";

/// GSSAPI mechanism types
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum GssapiMechanism {
    /// Kerberos 5
    Kerberos5,
    /// NTLM (Windows)
    Ntlm,
    /// SPNEGO (negotiation)
    Spnego,
}

impl GssapiMechanism {
    /// Get OID for mechanism
    pub fn oid(&self) -> &[u8] {
        match self {
            Self::Kerberos5 => &[0x2a, 0x86, 0x48, 0x86, 0xf7, 0x12, 0x01, 0x02, 0x02],
            Self::Ntlm => &[0x2b, 0x06, 0x01, 0x04, 0x01, 0x82, 0x37, 0x02, 0x02, 0x0a],
            Self::Spnego => &[0x2b, 0x06, 0x01, 0x05, 0x05, 0x02],
        }
    }

    /// Parse from OID
    pub fn from_oid(oid: &[u8]) -> Option<Self> {
        if oid == Self::Kerberos5.oid() {
            Some(Self::Kerberos5)
        } else if oid == Self::Ntlm.oid() {
            Some(Self::Ntlm)
        } else if oid == Self::Spnego.oid() {
            Some(Self::Spnego)
        } else {
            None
        }
    }
}

/// GSSAPI context for authentication
///
/// **NOTE: This is a placeholder structure. GSSAPI authentication is not implemented.**
#[allow(dead_code)]
pub struct GssapiContext {
    /// Selected mechanism
    mechanism: GssapiMechanism,
    /// Context state
    state: ContextState,
    /// Service principal name
    service_name: String,
    /// Client principal name
    client_name: Option<String>,
    /// Session key (unused - GSSAPI not implemented)
    session_key: Option<Vec<u8>>,
    /// Context flags (unused - GSSAPI not implemented)
    flags: ContextFlags,
    /// Delegation credentials
    delegated_creds: Option<DelegatedCredentials>,
    /// Message integrity check (unused - GSSAPI not implemented)
    mic_token: Option<Vec<u8>>,
}

/// Context state
#[derive(Debug, Clone, PartialEq, Eq)]
enum ContextState {
    /// Initial state
    Initial,
    /// Waiting for server token
    WaitingForServer,
    /// Waiting for client token
    WaitingForClient,
    /// Context established
    Established,
    /// Error occurred
    Error(String),
}

/// Context flags
#[derive(Debug, Clone, Default)]
pub struct ContextFlags {
    /// Request mutual authentication
    pub mutual_auth: bool,
    /// Request confidentiality
    pub confidentiality: bool,
    /// Request integrity
    pub integrity: bool,
    /// Request anonymity
    pub anonymity: bool,
    /// Request delegation
    pub delegation: bool,
    /// Request replay detection
    pub replay_detection: bool,
    /// Request sequence detection
    pub sequence_detection: bool,
}

/// Delegated credentials
#[derive(Debug, Clone)]
pub struct DelegatedCredentials {
    /// Credential cache
    pub cache: Vec<u8>,
    /// Expiration time
    pub expiration: SystemTime,
}

impl GssapiContext {
    /// Create new GSSAPI context for client
    pub fn new_client(service_name: String, mechanism: GssapiMechanism) -> Self {
        Self {
            mechanism,
            state: ContextState::Initial,
            service_name,
            client_name: None,
            session_key: None,
            flags: ContextFlags::default(),
            delegated_creds: None,
            mic_token: None,
        }
    }

    /// Create new GSSAPI context for server
    pub fn new_server(mechanism: GssapiMechanism) -> Self {
        Self {
            mechanism,
            state: ContextState::Initial,
            service_name: String::new(),
            client_name: None,
            session_key: None,
            flags: ContextFlags::default(),
            delegated_creds: None,
            mic_token: None,
        }
    }

    /// Initialize security context (client)
    ///
    /// **NOTE: This is a placeholder implementation. GSSAPI is not functional.**
    pub fn init_sec_context(&mut self, _input_token: Option<&[u8]>) -> Result<GssapiToken> {
        // GSSAPI is not implemented - return a clear error
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Accept security context (server)
    ///
    /// **NOTE: This is a placeholder implementation. GSSAPI is not functional.**
    pub fn accept_sec_context(&mut self, _input_token: &[u8]) -> Result<GssapiToken> {
        // GSSAPI is not implemented - return a clear error
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Check if context is established
    ///
    /// **NOTE: GSSAPI is not implemented, so this will always return false.**
    pub fn is_established(&self) -> bool {
        self.state == ContextState::Established
    }

    /// Get client name
    pub fn client_name(&self) -> Option<&str> {
        self.client_name.as_deref()
    }

    /// Get delegated credentials
    pub fn delegated_credentials(&self) -> Option<&DelegatedCredentials> {
        self.delegated_creds.as_ref()
    }

    /// Create message integrity check token
    ///
    /// **NOTE: GSSAPI is not implemented. This will return an error.**
    pub fn get_mic(&self, _message: &[u8]) -> Result<Vec<u8>> {
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Verify message integrity check token
    ///
    /// **NOTE: GSSAPI is not implemented. This will return an error.**
    pub fn verify_mic(&self, _message: &[u8], _mic: &[u8]) -> Result<bool> {
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Wrap message for confidentiality
    ///
    /// **NOTE: GSSAPI is not implemented. This will return an error.**
    pub fn wrap(&self, _message: &[u8], _encrypt: bool) -> Result<Vec<u8>> {
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Unwrap message
    ///
    /// **NOTE: GSSAPI is not implemented. This will return an error.**
    pub fn unwrap(&self, _wrapped: &[u8]) -> Result<Vec<u8>> {
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }
}

/// GSSAPI token
#[derive(Debug, Clone)]
pub struct GssapiToken {
    /// Token data
    pub data: Vec<u8>,
    /// Whether context is complete
    pub complete: bool,
    /// Mechanism used
    pub mechanism: GssapiMechanism,
}

/// GSSAPI authenticator for SSH
///
/// **NOTE: This is a placeholder structure. GSSAPI authentication is not implemented.**
#[allow(dead_code)]
pub struct GssapiAuthenticator {
    /// Available mechanisms
    mechanisms: Vec<GssapiMechanism>,
    /// Active contexts
    contexts: HashMap<String, GssapiContext>,
    /// Service name (unused - GSSAPI not implemented)
    service_name: String,
}

impl GssapiAuthenticator {
    /// Create new authenticator
    ///
    /// **NOTE: GSSAPI is not implemented. All authentication attempts will fail.**
    pub fn new(service_name: String) -> Self {
        Self {
            mechanisms: vec![
                GssapiMechanism::Kerberos5,
                GssapiMechanism::Ntlm,
                GssapiMechanism::Spnego,
            ],
            contexts: HashMap::new(),
            service_name,
        }
    }

    /// Start authentication
    ///
    /// **NOTE: GSSAPI is not implemented. This will return an error.**
    pub fn start_auth(&mut self, _mechanism: GssapiMechanism, _client: bool) -> Result<String> {
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Continue authentication
    ///
    /// **NOTE: GSSAPI is not implemented. This will return an error.**
    pub fn continue_auth(&mut self, _context_id: &str, _input: Option<&[u8]>) -> Result<GssapiToken> {
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Accept authentication
    ///
    /// **NOTE: GSSAPI is not implemented. This will return an error.**
    pub fn accept_auth(&mut self, _context_id: &str, _input: &[u8]) -> Result<GssapiToken> {
        Err(QsshError::Protocol(GSSAPI_NOT_IMPLEMENTED.into()))
    }

    /// Get established context
    pub fn get_context(&self, context_id: &str) -> Option<&GssapiContext> {
        self.contexts.get(context_id)
    }

    /// List available mechanisms
    ///
    /// **NOTE: While mechanisms are listed, GSSAPI authentication is not functional.**
    pub fn available_mechanisms(&self) -> &[GssapiMechanism] {
        &self.mechanisms
    }
}

// Note: Full GSSAPI implementation (Kerberos, NTLM, SPNEGO message structures
// and encoding functions) has been removed as the feature is not functional.
// When implementing GSSAPI support, use a proper GSSAPI library like `gssapi` or `libgssapi`.

impl ContextFlags {
    /// Convert flags to bitmask (for protocol negotiation)
    pub fn to_bits(&self) -> u32 {
        let mut bits = 0;
        if self.mutual_auth { bits |= 0x01; }
        if self.confidentiality { bits |= 0x02; }
        if self.integrity { bits |= 0x04; }
        if self.anonymity { bits |= 0x08; }
        if self.delegation { bits |= 0x10; }
        if self.replay_detection { bits |= 0x20; }
        if self.sequence_detection { bits |= 0x40; }
        bits
    }
}

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

    #[test]
    fn test_mechanism_oids() {
        assert_eq!(GssapiMechanism::Kerberos5.oid().len(), 9);
        assert_eq!(GssapiMechanism::from_oid(GssapiMechanism::Kerberos5.oid()), Some(GssapiMechanism::Kerberos5));
    }

    #[test]
    fn test_context_creation() {
        let client = GssapiContext::new_client("host/server.example.com".to_string(), GssapiMechanism::Kerberos5);
        assert!(!client.is_established());

        let server = GssapiContext::new_server(GssapiMechanism::Kerberos5);
        assert!(!server.is_established());
    }

    #[test]
    fn test_authenticator_returns_error() {
        // GSSAPI is not implemented, so authentication should return an error
        let mut auth = GssapiAuthenticator::new("host/server.example.com".to_string());

        // start_auth should return an error since GSSAPI is not implemented
        let result = auth.start_auth(GssapiMechanism::Kerberos5, true);
        assert!(result.is_err());

        // Mechanisms are still listed for protocol negotiation purposes
        assert_eq!(auth.available_mechanisms().len(), 3);
    }

    #[test]
    fn test_init_sec_context_returns_error() {
        let mut context = GssapiContext::new_client("host/server.example.com".to_string(), GssapiMechanism::Kerberos5);
        let result = context.init_sec_context(None);
        assert!(result.is_err());
    }

    #[test]
    fn test_accept_sec_context_returns_error() {
        let mut context = GssapiContext::new_server(GssapiMechanism::Kerberos5);
        let result = context.accept_sec_context(&[0u8; 16]);
        assert!(result.is_err());
    }

    #[test]
    fn test_context_flags() {
        let mut flags = ContextFlags::default();
        flags.mutual_auth = true;
        flags.integrity = true;

        assert_eq!(flags.to_bits() & 0x01, 0x01);
        assert_eq!(flags.to_bits() & 0x04, 0x04);
    }
}