qssh 0.0.2-alpha

//! WARNING: This module contains placeholder implementations - DO NOT USE IN PRODUCTION
//! GSSAPI/Kerberos Authentication Support
//!
//! Implements GSSAPI authentication for enterprise environments with Kerberos

use std::collections::HashMap;
use std::time::{Duration, SystemTime, UNIX_EPOCH};
use crate::{Result, QsshError};
use base64::{Engine as _, engine::general_purpose::STANDARD as BASE64};

/// 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
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
    session_key: Option<Vec<u8>>,
    /// Context flags
    flags: ContextFlags,
    /// Delegation credentials
    delegated_creds: Option<DelegatedCredentials>,
    /// Message integrity check
    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)
    pub fn init_sec_context(&mut self, input_token: Option<&[u8]>) -> Result<GssapiToken> {
        match self.state {
            ContextState::Initial => {
                // Generate initial token based on mechanism
                let token = match self.mechanism {
                    GssapiMechanism::Kerberos5 => self.init_kerberos_context()?,
                    GssapiMechanism::Ntlm => self.init_ntlm_context()?,
                    GssapiMechanism::Spnego => self.init_spnego_context()?,
                };

                self.state = ContextState::WaitingForServer;
                Ok(token)
            }
            ContextState::WaitingForServer => {
                if let Some(server_token) = input_token {
                    // Process server token
                    let response = self.process_server_token(server_token)?;

                    if response.complete {
                        self.state = ContextState::Established;
                    }

                    Ok(response)
                } else {
                    Err(QsshError::Protocol("Expected server token".into()))
                }
            }
            ContextState::Established => {
                Ok(GssapiToken {
                    data: Vec::new(),
                    complete: true,
                    mechanism: self.mechanism,
                })
            }
            _ => Err(QsshError::Protocol("Invalid context state".into())),
        }
    }

    /// Accept security context (server)
    pub fn accept_sec_context(&mut self, input_token: &[u8]) -> Result<GssapiToken> {
        match self.state {
            ContextState::Initial => {
                // Process client's initial token
                let response = self.process_client_token(input_token)?;

                if response.complete {
                    self.state = ContextState::Established;
                } else {
                    self.state = ContextState::WaitingForClient;
                }

                Ok(response)
            }
            ContextState::WaitingForClient => {
                // Process additional client token
                let response = self.process_client_token(input_token)?;

                if response.complete {
                    self.state = ContextState::Established;
                }

                Ok(response)
            }
            ContextState::Established => {
                Ok(GssapiToken {
                    data: Vec::new(),
                    complete: true,
                    mechanism: self.mechanism,
                })
            }
            _ => Err(QsshError::Protocol("Invalid context state".into())),
        }
    }

    /// Initialize Kerberos context
    fn init_kerberos_context(&mut self) -> Result<GssapiToken> {
        // Simplified Kerberos initialization
        // In production, this would use actual Kerberos libraries

        // Create AP-REQ message
        let ap_req = KerberosApReq {
            pvno: 5,
            msg_type: 14, // AP-REQ
            ap_options: 0x40000000, // Mutual authentication
            ticket: self.get_service_ticket()?,
            authenticator: self.create_authenticator()?,
        };

        Ok(GssapiToken {
            data: encode_kerberos_message(&ap_req)?,
            complete: false,
            mechanism: GssapiMechanism::Kerberos5,
        })
    }

    /// Initialize NTLM context
    fn init_ntlm_context(&mut self) -> Result<GssapiToken> {
        // Simplified NTLM Type 1 message
        let type1 = NtlmType1Message {
            signature: b"NTLMSSP\0".to_vec(),
            message_type: 1,
            flags: 0x00000207, // Negotiate flags
            domain: String::new(),
            workstation: hostname::get()
                .unwrap_or_default()
                .to_string_lossy()
                .to_string(),
        };

        Ok(GssapiToken {
            data: encode_ntlm_message(&type1)?,
            complete: false,
            mechanism: GssapiMechanism::Ntlm,
        })
    }

    /// Initialize SPNEGO context
    fn init_spnego_context(&mut self) -> Result<GssapiToken> {
        // SPNEGO negotiation token
        let nego = SpnegoNegTokenInit {
            mech_types: vec![
                GssapiMechanism::Kerberos5.oid().to_vec(),
                GssapiMechanism::Ntlm.oid().to_vec(),
            ],
            req_flags: self.flags.to_bits(),
            mech_token: None,
            mech_list_mic: None,
        };

        Ok(GssapiToken {
            data: encode_spnego_message(&nego)?,
            complete: false,
            mechanism: GssapiMechanism::Spnego,
        })
    }

    /// Process server token
    fn process_server_token(&mut self, token: &[u8]) -> Result<GssapiToken> {
        match self.mechanism {
            GssapiMechanism::Kerberos5 => self.process_kerberos_response(token),
            GssapiMechanism::Ntlm => self.process_ntlm_challenge(token),
            GssapiMechanism::Spnego => self.process_spnego_response(token),
        }
    }

    /// Process client token
    fn process_client_token(&mut self, token: &[u8]) -> Result<GssapiToken> {
        match self.mechanism {
            GssapiMechanism::Kerberos5 => self.process_kerberos_request(token),
            GssapiMechanism::Ntlm => self.process_ntlm_auth(token),
            GssapiMechanism::Spnego => self.process_spnego_request(token),
        }
    }

    /// Process Kerberos response (AP-REP)
    fn process_kerberos_response(&mut self, token: &[u8]) -> Result<GssapiToken> {
        // Derive session key from token using SHA256
        use sha2::{Sha256, Digest};

        let mut hasher = Sha256::new();
        hasher.update(b"qssh-gssapi-session");
        hasher.update(token);
        let hash = hasher.finalize();
        let session_key = hash.to_vec();

        self.session_key = Some(session_key);

        Ok(GssapiToken {
            data: Vec::new(),
            complete: true,
            mechanism: GssapiMechanism::Kerberos5,
        })
    }

    /// Process Kerberos request (AP-REQ)
    fn process_kerberos_request(&mut self, token: &[u8]) -> Result<GssapiToken> {
        // Extract client name from token (simplified)
        let client_name = if token.len() > 20 {
            format!("user_{}@REALM.COM", hex::encode(&token[0..4]))
        } else {
            "user@REALM.COM".to_string()
        };
        self.client_name = Some(client_name);

        // Derive session key from token
        use sha2::{Sha256, Digest};
        let mut hasher = Sha256::new();
        hasher.update(b"qssh-kerberos-session");
        hasher.update(token);
        hasher.update(self.client_name.as_ref().unwrap_or(&String::new()).as_bytes());
        let hash = hasher.finalize();
        let session_key = hash.to_vec();

        self.session_key = Some(session_key);

        // Create AP-REP response
        let ap_rep = KerberosApRep {
            pvno: 5,
            msg_type: 15, // AP-REP
            enc_part: Vec::new(), // Would contain encrypted part
        };

        Ok(GssapiToken {
            data: encode_kerberos_message(&ap_rep)?,
            complete: true,
            mechanism: GssapiMechanism::Kerberos5,
        })
    }

    /// Process NTLM Type 2 challenge
    fn process_ntlm_challenge(&mut self, token: &[u8]) -> Result<GssapiToken> {
        // Parse Type 2 message and create Type 3 response
        let type3 = NtlmType3Message {
            signature: b"NTLMSSP\0".to_vec(),
            message_type: 3,
            lm_response: Vec::new(),
            ntlm_response: Vec::new(),
            domain: String::new(),
            username: whoami::username(),
            workstation: hostname::get()
                .unwrap_or_default()
                .to_string_lossy()
                .to_string(),
            session_key: Vec::new(),
        };

        Ok(GssapiToken {
            data: encode_ntlm_message(&type3)?,
            complete: true,
            mechanism: GssapiMechanism::Ntlm,
        })
    }

    /// Process NTLM authentication
    fn process_ntlm_auth(&mut self, _token: &[u8]) -> Result<GssapiToken> {
        // Verify NTLM credentials
        self.client_name = Some("DOMAIN\\user".to_string());

        Ok(GssapiToken {
            data: Vec::new(),
            complete: true,
            mechanism: GssapiMechanism::Ntlm,
        })
    }

    /// Process SPNEGO response
    fn process_spnego_response(&mut self, _token: &[u8]) -> Result<GssapiToken> {
        Ok(GssapiToken {
            data: Vec::new(),
            complete: true,
            mechanism: GssapiMechanism::Spnego,
        })
    }

    /// Process SPNEGO request
    fn process_spnego_request(&mut self, _token: &[u8]) -> Result<GssapiToken> {
        Ok(GssapiToken {
            data: Vec::new(),
            complete: true,
            mechanism: GssapiMechanism::Spnego,
        })
    }

    /// Get service ticket (Kerberos)
    fn get_service_ticket(&self) -> Result<Vec<u8>> {
        // TODO: Implement actual Kerberos ticket fetching
        Err(QsshError::Protocol("Kerberos service tickets not implemented".into()))
    }

    /// Create authenticator (Kerberos)
    fn create_authenticator(&self) -> Result<Vec<u8>> {
        // TODO: Implement actual Kerberos authenticator creation
        Err(QsshError::Protocol("Kerberos authenticators not implemented".into()))
    }

    /// Create message integrity check token
    pub fn get_mic(&self, message: &[u8]) -> Result<Vec<u8>> {
        if !self.is_established() {
            return Err(QsshError::Protocol("Context not established".into()));
        }

        // Simplified MIC calculation
        use sha2::{Sha256, Digest};
        let mut hasher = Sha256::new();
        hasher.update(message);
        if let Some(key) = &self.session_key {
            hasher.update(key);
        }
        Ok(hasher.finalize().to_vec())
    }

    /// Verify message integrity check token
    pub fn verify_mic(&self, message: &[u8], mic: &[u8]) -> Result<bool> {
        let expected = self.get_mic(message)?;
        Ok(expected == mic)
    }

    /// Wrap message for confidentiality
    pub fn wrap(&self, message: &[u8], encrypt: bool) -> Result<Vec<u8>> {
        if !self.is_established() {
            return Err(QsshError::Protocol("Context not established".into()));
        }

        if encrypt && self.flags.confidentiality {
            // Would encrypt with session key
            Ok(message.to_vec()) // Placeholder
        } else {
            // Just add integrity protection
            let mic = self.get_mic(message)?;
            let mut wrapped = message.to_vec();
            wrapped.extend_from_slice(&mic);
            Ok(wrapped)
        }
    }

    /// Unwrap message
    pub fn unwrap(&self, wrapped: &[u8]) -> Result<Vec<u8>> {
        if !self.is_established() {
            return Err(QsshError::Protocol("Context not established".into()));
        }

        // Simplified - would decrypt or verify integrity
        Ok(wrapped.to_vec())
    }

    /// Check if context is established
    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()
    }
}

/// 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
pub struct GssapiAuthenticator {
    /// Available mechanisms
    mechanisms: Vec<GssapiMechanism>,
    /// Active contexts
    contexts: HashMap<String, GssapiContext>,
    /// Service name
    service_name: String,
}

impl GssapiAuthenticator {
    /// Create new authenticator
    pub fn new(service_name: String) -> Self {
        Self {
            mechanisms: vec![
                GssapiMechanism::Kerberos5,
                GssapiMechanism::Ntlm,
                GssapiMechanism::Spnego,
            ],
            contexts: HashMap::new(),
            service_name,
        }
    }

    /// Start authentication
    pub fn start_auth(&mut self, mechanism: GssapiMechanism, client: bool) -> Result<String> {
        let context_id = generate_context_id();

        let context = if client {
            GssapiContext::new_client(self.service_name.clone(), mechanism)
        } else {
            GssapiContext::new_server(mechanism)
        };

        self.contexts.insert(context_id.clone(), context);
        Ok(context_id)
    }

    /// Continue authentication
    pub fn continue_auth(&mut self, context_id: &str, input: Option<&[u8]>) -> Result<GssapiToken> {
        let context = self.contexts.get_mut(context_id)
            .ok_or_else(|| QsshError::Protocol("Invalid context ID".into()))?;

        context.init_sec_context(input)
    }

    /// Accept authentication
    pub fn accept_auth(&mut self, context_id: &str, input: &[u8]) -> Result<GssapiToken> {
        let context = self.contexts.get_mut(context_id)
            .ok_or_else(|| QsshError::Protocol("Invalid context ID".into()))?;

        context.accept_sec_context(input)
    }

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

    /// List available mechanisms
    pub fn available_mechanisms(&self) -> &[GssapiMechanism] {
        &self.mechanisms
    }
}

// Message structures (simplified)

struct KerberosApReq {
    pvno: u8,
    msg_type: u8,
    ap_options: u32,
    ticket: Vec<u8>,
    authenticator: Vec<u8>,
}

struct KerberosApRep {
    pvno: u8,
    msg_type: u8,
    enc_part: Vec<u8>,
}

struct NtlmType1Message {
    signature: Vec<u8>,
    message_type: u32,
    flags: u32,
    domain: String,
    workstation: String,
}

struct NtlmType3Message {
    signature: Vec<u8>,
    message_type: u32,
    lm_response: Vec<u8>,
    ntlm_response: Vec<u8>,
    domain: String,
    username: String,
    workstation: String,
    session_key: Vec<u8>,
}

struct SpnegoNegTokenInit {
    mech_types: Vec<Vec<u8>>,
    req_flags: u32,
    mech_token: Option<Vec<u8>>,
    mech_list_mic: Option<Vec<u8>>,
}

// Helper functions

fn generate_context_id() -> String {
    use rand::Rng;
    let mut rng = rand::thread_rng();
    let bytes: Vec<u8> = (0..16).map(|_| rng.gen()).collect();
    hex::encode(bytes)
}

fn encode_kerberos_message<T>(_msg: &T) -> Result<Vec<u8>> {
    Err(QsshError::Protocol(
        "Kerberos message encoding not implemented".into()
    ))
}

fn encode_ntlm_message<T>(_msg: &T) -> Result<Vec<u8>> {
    Err(QsshError::Protocol(
        "NTLM message encoding not implemented".into()
    ))
}

fn encode_spnego_message<T>(_msg: &T) -> Result<Vec<u8>> {
    Err(QsshError::Protocol(
        "SPNEGO message encoding not implemented".into()
    ))
}

impl ContextFlags {
    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 mut 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() {
        let mut auth = GssapiAuthenticator::new("host/server.example.com".to_string());

        let context_id = auth.start_auth(GssapiMechanism::Kerberos5, true).unwrap();
        assert!(auth.get_context(&context_id).is_some());

        assert_eq!(auth.available_mechanisms().len(), 3);
    }

    #[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);
    }
}