dragoon-server 0.1.0

//! Authentication primitives: password hashing, TOTP, recovery codes,
//! session / challenge / nonce lifecycle.
//!
//! The full per-request signature pipeline (`verify_signed_request`) lives
//! at the bottom of this file; Phase 6 plugs it into an axum middleware.
//! Mirrors `python/.../server/auth.py`.

use std::time::{SystemTime, UNIX_EPOCH};

use anyhow::{anyhow, Context, Result};
use argon2::password_hash::{rand_core::OsRng as ArgonOsRng, PasswordHasher, PasswordVerifier, SaltString};
use argon2::{Algorithm, Argon2, Params, PasswordHash, Version};
use base64::{
    engine::general_purpose::{STANDARD as B64, URL_SAFE_NO_PAD as B64URL},
    Engine,
};
use chrono::{DateTime, Duration, Utc};
use rand::{rngs::OsRng as RandOsRng, RngCore};
use rusqlite::{params, Connection, OptionalExtension};
use sha2::{Digest, Sha256};
use thiserror::Error;
use totp_rs::{Algorithm as TotpAlg, TOTP};

use dragoon_proto::{constants, verify::verify_ssh_wire_signature};

// --------------------------------------------------------------------------
// Password (argon2id)
// --------------------------------------------------------------------------

fn argon2() -> Argon2<'static> {
    // Pinned params (m=65536 KiB, t=3, p=4) for new hashes. Verifying older
    // hashes uses whatever params the PHC string carries so Python-produced
    // hashes (which use argon2-cffi defaults) still verify.
    let params = Params::new(65_536, 3, 4, None).expect("argon2 params are valid");
    Argon2::new(Algorithm::Argon2id, Version::V0x13, params)
}

pub fn hash_password(plain: &str) -> Result<String> {
    let salt = SaltString::generate(&mut ArgonOsRng);
    let hash = argon2()
        .hash_password(plain.as_bytes(), &salt)
        .map_err(|e| anyhow!("argon2 hash: {e}"))?;
    Ok(hash.to_string())
}

pub fn verify_password(plain: &str, hashed: &str) -> bool {
    let Ok(parsed) = PasswordHash::new(hashed) else {
        return false;
    };
    Argon2::default()
        .verify_password(plain.as_bytes(), &parsed)
        .is_ok()
}

// --------------------------------------------------------------------------
// TOTP (RFC 6238, ±1 step)
// --------------------------------------------------------------------------

pub fn generate_totp_secret() -> String {
    // 160-bit base32 secret, matching pyotp.random_base32().
    let mut bytes = [0u8; 20];
    RandOsRng.fill_bytes(&mut bytes);
    base32_encode_no_pad(&bytes)
}

pub fn verify_totp(secret_base32: &str, code: &str) -> bool {
    let Some(secret_bytes) = base32_decode(secret_base32) else {
        return false;
    };
    let Ok(totp) = TOTP::new(TotpAlg::SHA1, 6, 1, 30, secret_bytes) else {
        return false;
    };
    let Ok(now) = SystemTime::now().duration_since(UNIX_EPOCH) else {
        return false;
    };
    let now = now.as_secs();
    // ±1 step window
    for offset in [-1i64, 0, 1] {
        let t = (now as i64 + offset * 30).max(0) as u64;
        let want = totp.generate(t);
        if want == code {
            return true;
        }
    }
    false
}

const B32: &[u8; 32] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";

fn base32_encode_no_pad(input: &[u8]) -> String {
    let mut out = String::new();
    let mut buffer: u32 = 0;
    let mut bits = 0u32;
    for &b in input {
        buffer = (buffer << 8) | u32::from(b);
        bits += 8;
        while bits >= 5 {
            bits -= 5;
            let idx = ((buffer >> bits) & 0x1f) as usize;
            out.push(B32[idx] as char);
        }
    }
    if bits > 0 {
        let idx = ((buffer << (5 - bits)) & 0x1f) as usize;
        out.push(B32[idx] as char);
    }
    out
}

fn base32_decode(s: &str) -> Option<Vec<u8>> {
    let mut out = Vec::with_capacity(s.len() * 5 / 8);
    let mut buffer: u32 = 0;
    let mut bits = 0u32;
    for c in s.chars() {
        if c == '=' {
            break;
        }
        let v = match c {
            'A'..='Z' => (c as u8) - b'A',
            'a'..='z' => (c as u8) - b'a',
            '2'..='7' => (c as u8) - b'2' + 26,
            _ => return None,
        };
        buffer = (buffer << 5) | u32::from(v);
        bits += 5;
        if bits >= 8 {
            bits -= 8;
            out.push(((buffer >> bits) & 0xff) as u8);
        }
    }
    Some(out)
}

// --------------------------------------------------------------------------
// Recovery codes
// --------------------------------------------------------------------------

fn token_urlsafe(byte_len: usize) -> String {
    let mut bytes = vec![0u8; byte_len];
    RandOsRng.fill_bytes(&mut bytes);
    B64URL.encode(&bytes)
}

fn sha256_hex(input: &str) -> String {
    let digest = Sha256::digest(input.as_bytes());
    hex::encode(digest)
}

pub fn generate_recovery_codes(n: usize) -> (Vec<String>, Vec<String>) {
    let plain: Vec<String> = (0..n).map(|_| token_urlsafe(10)).collect();
    let hashes: Vec<String> = plain.iter().map(|c| sha256_hex(c)).collect();
    (plain, hashes)
}

pub fn consume_recovery_code(code: &str, hashes: &[String]) -> (bool, Vec<String>) {
    let h = sha256_hex(code);
    if !hashes.iter().any(|x| x == &h) {
        return (false, hashes.to_vec());
    }
    (true, hashes.iter().filter(|x| **x != h).cloned().collect())
}

// --------------------------------------------------------------------------
// Sessions
// --------------------------------------------------------------------------

#[derive(Debug, Clone)]
pub struct Session {
    pub user_id: i64,
    pub fingerprint: String,
    pub expires_at: DateTime<Utc>,
}

fn iso_now() -> String {
    Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Micros, true)
}

fn iso(dt: DateTime<Utc>) -> String {
    dt.to_rfc3339_opts(chrono::SecondsFormat::Micros, true)
}

fn parse_iso(s: &str) -> Result<DateTime<Utc>> {
    let s = if let Some(stripped) = s.strip_suffix('Z') {
        format!("{stripped}+00:00")
    } else {
        s.to_owned()
    };
    Ok(DateTime::parse_from_rfc3339(&s)
        .with_context(|| format!("parse rfc3339: {s}"))?
        .with_timezone(&Utc))
}

fn hash_token(token: &str) -> String {
    sha256_hex(token)
}

pub fn issue_session(
    conn: &Connection,
    user_id: i64,
    fingerprint: &str,
    ttl: Duration,
) -> Result<(String, DateTime<Utc>)> {
    let token = token_urlsafe(32);
    let h = hash_token(&token);
    let now = Utc::now();
    let expires = now + ttl;
    conn.execute(
        "INSERT INTO sessions (token_hash, user_id, fingerprint, created_at, expires_at)
         VALUES (?,?,?,?,?)",
        params![h, user_id, fingerprint, iso(now), iso(expires)],
    )?;
    Ok((token, expires))
}

pub fn lookup_session(conn: &Connection, token: &str) -> Result<Option<Session>> {
    let h = hash_token(token);
    let row: Option<(i64, String, String, Option<String>)> = conn
        .query_row(
            "SELECT user_id, fingerprint, expires_at, revoked_at
             FROM sessions WHERE token_hash=?",
            [h],
            |r| Ok((r.get(0)?, r.get(1)?, r.get(2)?, r.get(3)?)),
        )
        .optional()?;
    let Some((user_id, fingerprint, expires_at, revoked_at)) = row else {
        return Ok(None);
    };
    if revoked_at.is_some() {
        return Ok(None);
    }
    let expires = parse_iso(&expires_at)?;
    if expires <= Utc::now() {
        return Ok(None);
    }
    Ok(Some(Session {
        user_id,
        fingerprint,
        expires_at: expires,
    }))
}

pub fn revoke_session(conn: &Connection, token: &str) -> Result<()> {
    let h = hash_token(token);
    conn.execute(
        "UPDATE sessions SET revoked_at=? WHERE token_hash=?",
        params![iso_now(), h],
    )?;
    Ok(())
}

// --------------------------------------------------------------------------
// Challenges (one-shot per login)
// --------------------------------------------------------------------------

#[derive(Debug, Clone)]
pub struct IssuedChallenge {
    pub challenge: String,
    pub expires_at: DateTime<Utc>,
}

pub fn issue_challenge(conn: &Connection, ttl_sec: Option<i64>) -> Result<IssuedChallenge> {
    let ttl = ttl_sec.unwrap_or(constants::CHALLENGE_TTL_SEC);
    let challenge = token_urlsafe(16);
    let expires = Utc::now() + Duration::seconds(ttl);
    conn.execute(
        "INSERT INTO challenges (challenge, expires_at, used_at) VALUES (?,?,NULL)",
        params![challenge, iso(expires)],
    )?;
    Ok(IssuedChallenge {
        challenge,
        expires_at: expires,
    })
}

pub fn consume_challenge(conn: &Connection, challenge: &str) -> Result<bool> {
    let row: Option<(String, Option<String>)> = conn
        .query_row(
            "SELECT expires_at, used_at FROM challenges WHERE challenge=?",
            [challenge],
            |r| Ok((r.get(0)?, r.get(1)?)),
        )
        .optional()?;
    let Some((expires_at, used_at)) = row else {
        return Ok(false);
    };
    if used_at.is_some() {
        return Ok(false);
    }
    if parse_iso(&expires_at)? <= Utc::now() {
        return Ok(false);
    }
    let n = conn.execute(
        "UPDATE challenges SET used_at=? WHERE challenge=? AND used_at IS NULL",
        params![iso_now(), challenge],
    )?;
    Ok(n > 0)
}

// --------------------------------------------------------------------------
// Nonces (per-user, replay defense)
// --------------------------------------------------------------------------

pub fn consume_nonce(
    conn: &Connection,
    user_id: i64,
    nonce: &str,
    ttl_sec: i64,
) -> Result<bool> {
    let expires = Utc::now() + Duration::seconds(ttl_sec);
    let r = conn.execute(
        "INSERT INTO nonces (user_id, nonce, expires_at) VALUES (?,?,?)",
        params![user_id, nonce, iso(expires)],
    );
    match r {
        Ok(_) => Ok(true),
        Err(rusqlite::Error::SqliteFailure(err, _))
            if err.code == rusqlite::ErrorCode::ConstraintViolation =>
        {
            Ok(false)
        }
        Err(e) => Err(e.into()),
    }
}

pub fn purge_expired_nonces(conn: &Connection) -> Result<usize> {
    Ok(conn.execute(
        "DELETE FROM nonces WHERE expires_at<?",
        params![iso_now()],
    )?)
}

// --------------------------------------------------------------------------
// Per-request signature verification (design §7.2)
// --------------------------------------------------------------------------

#[derive(Debug, Error, Clone, PartialEq, Eq)]
pub enum AuthError {
    #[error("no_session")]
    NoSession,
    #[error("clock_skew")]
    ClockSkew,
    #[error("fp_session_mismatch")]
    FpSessionMismatch,
    #[error("unknown_fp")]
    UnknownFingerprint,
    #[error("revoked_fp")]
    RevokedFingerprint,
    #[error("replay")]
    Replay,
    #[error("bad_sig")]
    BadSignature,
}

impl AuthError {
    pub fn reason(&self) -> &'static str {
        match self {
            Self::NoSession => "no_session",
            Self::ClockSkew => "clock_skew",
            Self::FpSessionMismatch => "fp_session_mismatch",
            Self::UnknownFingerprint => "unknown_fp",
            Self::RevokedFingerprint => "revoked_fp",
            Self::Replay => "replay",
            Self::BadSignature => "bad_sig",
        }
    }
}

#[allow(clippy::too_many_arguments)]
pub fn verify_signed_request(
    conn: &Connection,
    session_token: &str,
    method: &str,
    path: &str,
    timestamp: i64,
    nonce: &str,
    key_fingerprint: &str,
    signature_b64: &str,
    body: &[u8],
    now: Option<i64>,
) -> std::result::Result<Session, AuthError> {
    let actual_now = now.unwrap_or_else(|| {
        i64::try_from(
            SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .map(|d| d.as_secs())
                .unwrap_or(0),
        )
        .unwrap_or(0)
    });

    let sess = lookup_session(conn, session_token)
        .map_err(|_| AuthError::NoSession)?
        .ok_or(AuthError::NoSession)?;

    if (actual_now - timestamp).abs() > constants::TIMESTAMP_SKEW_SEC {
        return Err(AuthError::ClockSkew);
    }

    if sess.fingerprint != key_fingerprint {
        return Err(AuthError::FpSessionMismatch);
    }

    let row: Option<(Vec<u8>, Option<String>)> = conn
        .query_row(
            "SELECT pubkey_blob, revoked_at FROM user_pubkeys
             WHERE user_id=? AND fingerprint=?",
            params![sess.user_id, key_fingerprint],
            |r| Ok((r.get(0)?, r.get(1)?)),
        )
        .optional()
        .map_err(|_| AuthError::UnknownFingerprint)?;
    let Some((pub_blob, revoked_at)) = row else {
        return Err(AuthError::UnknownFingerprint);
    };
    if revoked_at.is_some() {
        return Err(AuthError::RevokedFingerprint);
    }

    let fresh = consume_nonce(conn, sess.user_id, nonce, constants::NONCE_TTL_SEC)
        .map_err(|_| AuthError::Replay)?;
    if !fresh {
        return Err(AuthError::Replay);
    }

    let canonical = dragoon_proto::canonical::canonical_string(method, path, timestamp, nonce, body);
    let sig_wire = B64.decode(signature_b64).map_err(|_| AuthError::BadSignature)?;
    verify_ssh_wire_signature(&pub_blob, &sig_wire, &canonical)
        .map_err(|_| AuthError::BadSignature)?;
    Ok(sess)
}

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

    fn fresh() -> Connection {
        let c = crate::db::connect_in_memory().unwrap();
        crate::db::bootstrap(&c).unwrap();
        c
    }

    #[test]
    fn argon2_hash_then_verify() {
        let h = hash_password("hunter2").unwrap();
        assert!(h.starts_with("$argon2id$"));
        assert!(verify_password("hunter2", &h));
        assert!(!verify_password("wrong", &h));
    }

    #[test]
    fn totp_round_trip() {
        let s = generate_totp_secret();
        // base32 decode round-trip
        assert!(base32_decode(&s).is_some());

        let secret_bytes = base32_decode(&s).unwrap();
        let totp = TOTP::new(TotpAlg::SHA1, 6, 1, 30, secret_bytes).unwrap();
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_secs();
        let code: String = totp.generate(now);
        assert!(verify_totp(&s, &code));
        assert!(!verify_totp(&s, "000000"));
    }

    #[test]
    fn recovery_codes_consume_once() {
        let (plain, hashes) = generate_recovery_codes(3);
        let (ok, remaining) = consume_recovery_code(&plain[1], &hashes);
        assert!(ok);
        assert_eq!(remaining.len(), 2);
        let (ok2, _) = consume_recovery_code(&plain[1], &remaining);
        assert!(!ok2);
    }

    #[test]
    fn session_round_trip_then_revoke() {
        let c = fresh();
        c.execute(
            "INSERT INTO users (username, password_hash, totp_secret_enc, created_at)
             VALUES (?,?,?,?)",
            params!["alice", "h", "s", "2026-01-01T00:00:00Z"],
        )
        .unwrap();
        let uid = c.last_insert_rowid();
        let (tok, _) = issue_session(&c, uid, "SHA256:fp", Duration::hours(1)).unwrap();
        let sess = lookup_session(&c, &tok).unwrap().unwrap();
        assert_eq!(sess.user_id, uid);
        assert_eq!(sess.fingerprint, "SHA256:fp");
        revoke_session(&c, &tok).unwrap();
        assert!(lookup_session(&c, &tok).unwrap().is_none());
    }

    #[test]
    fn challenge_one_shot() {
        let c = fresh();
        let ch = issue_challenge(&c, None).unwrap();
        assert!(consume_challenge(&c, &ch.challenge).unwrap());
        assert!(!consume_challenge(&c, &ch.challenge).unwrap());
    }

    #[test]
    fn nonce_rejected_on_replay() {
        let c = fresh();
        c.execute(
            "INSERT INTO users (username, password_hash, totp_secret_enc, created_at)
             VALUES (?,?,?,?)",
            params!["u", "h", "s", "2026-01-01T00:00:00Z"],
        )
        .unwrap();
        let uid = c.last_insert_rowid();
        assert!(consume_nonce(&c, uid, "abc", 300).unwrap());
        assert!(!consume_nonce(&c, uid, "abc", 300).unwrap());
    }
}