tablo-core 0.10.0

//! Two-factor sign-in: the [`TwoFactor`] a panel installs, the [`AuthFactor`] rows that hold each
//! account's authenticator secret and recovery codes, and the checks the challenge and settings
//! pages run against them.

mod backoff;
mod challenge;
mod cipher;
mod email;
mod pages;
mod settings;
mod totp;

use std::{any::Any, sync::Arc, time::Duration};

use jiff::Timestamp;
use subtle::ConstantTimeEq;
use topcoat::{
    context::{Cx, try_context},
    cookie::Key,
};

pub(crate) use self::{challenge::challenge_url, settings::settings_url};
pub(super) use self::{
    challenge::{begin as begin_challenge, challenge_page, challenge_post},
    settings::{settings_page, settings_post},
};
use super::{LoginThrottle, PanelUser, infrastructure_failure};
use crate::auth::realm::{Realm, panel_prefix};

/// A panel's two-factor sign-in, installed with [`Auth::two_factor`](super::Auth::two_factor):
/// each signed-in user may add an authenticator app, or codes by email when the panel mails them,
/// at `{prefix}/two-factor`, and an account that has one signs in with a code from it after its
/// password.
///
/// ```rust
/// use tablo_core::{Auth, TwoFactor};
///
/// let auth = Auth::password().two_factor(TwoFactor::new().required());
/// # let _ = auth;
/// ```
#[derive(Debug)]
pub struct TwoFactor {
    required: Requirement,
    email: bool,
    pub(in crate::auth) throttle: LoginThrottle,
    pub(in crate::auth) mail_throttle: LoginThrottle,
}

impl TwoFactor {
    /// Two-factor sign-in each user may turn on.
    #[must_use]
    pub fn new() -> Self {
        Self {
            required: Requirement::Nobody,
            email: false,
            throttle: LoginThrottle::new(5, Duration::from_mins(1)),
            mail_throttle: LoginThrottle::new(3, Duration::from_mins(15)),
        }
    }

    /// Sends a signed-in user without a second factor to `{prefix}/two-factor` before anything
    /// else: a page answers with a redirect to it and any other request with 403, after an
    /// unverified address.
    #[must_use]
    pub fn required(mut self) -> Self {
        self.required = Requirement::Everyone;
        self
    }

    /// Requires a second factor of the users `rule` answers `true` for, as
    /// [`required`](Self::required) does of every user, and leaves it optional for the others:
    /// staff, say, or the members of a tenant that asks it of them.
    ///
    /// The rule is asked on every request, so a user it starts to cover is sent to set up a
    /// factor at their next one. A user of another type than `U` is required one: the panel
    /// signs in no such user, so the rule cannot have meant to let them through.
    ///
    /// ```rust
    /// use tablo_core::{Auth, TwoFactor, auth::AdminUser};
    ///
    /// let auth = Auth::password().two_factor(
    ///     TwoFactor::new()
    ///         .required_for(|_cx, user: &AdminUser| user.email.ends_with("@staff.example")),
    /// );
    /// # let _ = auth;
    /// ```
    #[must_use]
    pub fn required_for<U: PanelUser>(
        mut self,
        rule: impl Fn(&Cx, &U) -> bool + Send + Sync + 'static,
    ) -> Self {
        self.required = Requirement::Some(Arc::new(move |cx, user| {
            let user: &dyn Any = user;
            user.downcast_ref::<U>().is_none_or(|user| rule(cx, user))
        }));
        self
    }

    /// Lets a user with an address choose codes mailed to it in place of an authenticator app:
    /// each sign-in mails one, through [`Auth::mail`](super::Auth::mail), which mounting then
    /// requires. A mailed code works once, for ten minutes.
    #[must_use]
    pub fn email_codes(mut self) -> Self {
        self.email = true;
        self
    }

    /// How many codes one account may have mailed in a window; defaults to three in fifteen
    /// minutes.
    #[must_use]
    pub fn mail_throttle(mut self, throttle: LoginThrottle) -> Self {
        self.mail_throttle = throttle;
        self
    }

    /// How many codes one account may try in a window, from any client, at sign-in and on the
    /// settings page together; defaults to five a minute.
    #[must_use]
    pub fn throttle(mut self, throttle: LoginThrottle) -> Self {
        self.throttle = throttle;
        self
    }
}

impl TwoFactor {
    /// Whether the panel asks `user` for a second factor before anything else.
    fn requires(&self, cx: &Cx, user: &dyn PanelUser) -> bool {
        match &self.required {
            Requirement::Nobody => false,
            Requirement::Everyone => true,
            Requirement::Some(rule) => rule(cx, user),
        }
    }

    /// Whether the panel mails codes.
    pub(in crate::auth) fn mails(&self) -> bool {
        self.email
    }
}

/// The rule of [`TwoFactor::required_for`], with its user type erased.
type Rule = dyn Fn(&Cx, &dyn PanelUser) -> bool + Send + Sync;

/// Whom a [`TwoFactor`] requires a second factor of.
enum Requirement {
    Nobody,
    Everyone,
    Some(Arc<Rule>),
}

impl std::fmt::Debug for Requirement {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(match self {
            Self::Nobody => "Nobody",
            Self::Everyone => "Everyone",
            Self::Some(_) => "Some(..)",
        })
    }
}

impl Default for TwoFactor {
    fn default() -> Self {
        Self::new()
    }
}

/// Shipped second-factor record: an account's authenticator secret, sealed, or the hash of one of
/// its recovery codes, on the panel that enrolled it.
#[derive(Debug, Clone, toasty::Model)]
pub struct AuthFactor {
    #[key]
    #[auto]
    pub id: uuid::Uuid,
    /// [`PanelUser::user_id`](super::PanelUser::user_id) of the account the factor signs in.
    #[index]
    pub user_id: String,
    /// The prefix of the panel that enrolled the factor: the only panel it signs in to.
    pub panel: String,
    pub kind: FactorKind,
    /// The authenticator secret, sealed under the router's cookie key, or the hash of a recovery
    /// code, keyed under it.
    pub secret: String,
    /// When a code proved the authenticator app holds the secret; `None` while it is being set
    /// up. A recovery code is confirmed when issued.
    pub confirmed_at: Option<Timestamp>,
    /// The last 30-second step an authenticator code signed in with: a code works once.
    pub last_step: Option<i64>,
    /// The wrong codes in a row signing in since the last right one, on the confirmed factor.
    pub failures: i64,
    /// Until when signing in refuses the confirmed factor's codes after
    /// [`failures`](Self::failures) wrong ones; a recovery code still works.
    pub retry_at: Option<Timestamp>,
    pub created_at: Timestamp,
}

/// What an [`AuthFactor`] is. Stored as its `snake_case` name in a text column, so a kind a later
/// release adds needs no migration.
#[derive(Debug, Clone, Copy, PartialEq, Eq, toasty::Embed)]
#[column(type = text)]
#[non_exhaustive]
pub enum FactorKind {
    /// An authenticator app's RFC 6238 secret.
    Authenticator,
    /// A single-use recovery code, for an account that lost its authenticator.
    RecoveryCode,
    /// Codes mailed to the account's address, one per sign-in; the row holds no secret.
    EmailCode,
}

/// How many recovery codes a set-up or a regeneration issues.
const RECOVERY_CODES: usize = 8;

/// The characters a recovery code draws from: lowercase base32, which reads without ambiguity.
const RECOVERY_ALPHABET: &[u8; 32] = b"abcdefghijklmnopqrstuvwxyz234567";

/// The router's cookie key, which seals authenticator secrets.
fn key(cx: &Cx) -> topcoat::Result<&Key> {
    try_context::<Key>(cx)
        .ok_or_else(|| crate::error::declaration("two-factor sign-in needs the router's `Key`"))
}

/// What a sealed secret is bound to: its account on its panel.
fn binding(user_id: &str, panel: &str) -> String {
    format!("{user_id}\n{panel}")
}

/// Every factor `user_id` holds on the panel at `panel`, read through `ex`.
async fn factors(
    ex: &mut dyn toasty::Executor,
    panel: &str,
    user_id: &str,
) -> topcoat::Result<Vec<AuthFactor>> {
    AuthFactor::filter(
        AuthFactor::fields()
            .user_id()
            .eq(user_id.to_string())
            .and(AuthFactor::fields().panel().eq(panel.to_string())),
    )
    .exec(ex)
    .await
    .map_err(infrastructure_failure)
}

/// What `user_id` holds on the request's panel: the confirmed factor, an authenticator or mailed
/// codes, the one being set up, and how many recovery codes are left.
#[derive(Debug, Default)]
pub(super) struct Enrolment {
    pub(super) confirmed: Option<AuthFactor>,
    pub(super) unconfirmed: Option<AuthFactor>,
    pub(super) recovery_codes: usize,
}

/// `user_id`'s [`Enrolment`] on the request's panel.
pub(super) async fn enrolment(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    user_id: &str,
) -> topcoat::Result<Enrolment> {
    enrolment_on(ex, &panel_prefix(cx), user_id).await
}

/// `user_id`'s [`Enrolment`] on the panel at `panel`.
async fn enrolment_on(
    ex: &mut dyn toasty::Executor,
    panel: &str,
    user_id: &str,
) -> topcoat::Result<Enrolment> {
    let mut enrolment = Enrolment::default();
    for factor in factors(ex, panel, user_id).await? {
        match (factor.kind, factor.confirmed_at.is_some()) {
            (FactorKind::RecoveryCode, _) => enrolment.recovery_codes += 1,
            (_, true) => enrolment.confirmed = Some(factor),
            (_, false) => enrolment.unconfirmed = Some(factor),
        }
    }
    Ok(enrolment)
}

/// The kind of second factor `user` signs in to the request's panel with, if any.
pub(super) async fn enrolled(cx: &Cx, user: &dyn PanelUser) -> topcoat::Result<Option<FactorKind>> {
    let mut db = crate::db::db(cx)?;
    Ok(enrolment(cx, &mut db, &user.user_id())
        .await?
        .confirmed
        .map(|factor| factor.kind))
}

/// Whether the request's panel offers the signed-in user two-factor sign-in.
pub(crate) fn offered(cx: &Cx) -> bool {
    super::signed(cx).is_some_and(|signed| signed.realm.auth.two_factor_config().is_some())
}

/// Whether `panel` sends `user` to set up an authenticator before anything else: it requires one
/// of them, and the user holds none.
pub(super) async fn setup_pending(
    cx: &Cx,
    panel: &Realm,
    user: &dyn PanelUser,
) -> topcoat::Result<bool> {
    match panel.auth.two_factor_config() {
        Some(two_factor) if two_factor.requires(cx, user) => {
            let mut db = crate::db::db(cx)?;
            let enrolment = enrolment_on(&mut db, &panel.prefix, &user.user_id()).await?;
            Ok(enrolment.confirmed.is_none())
        }
        _ => Ok(false),
    }
}

/// Starts setting up a factor of `kind` holding `secret` for `user_id`, unconfirmed, in place of
/// any factor set up before and not confirmed.
async fn start(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    user_id: &str,
    kind: FactorKind,
    secret: String,
) -> topcoat::Result<()> {
    let panel = panel_prefix(cx);
    // A recovery code is confirmed when issued: only a factor being set up matches.
    AuthFactor::filter(
        AuthFactor::fields()
            .user_id()
            .eq(user_id.to_string())
            .and(AuthFactor::fields().panel().eq(panel.clone()))
            .and(AuthFactor::fields().confirmed_at().is_none()),
    )
    .delete()
    .exec(&mut *ex)
    .await
    .map_err(infrastructure_failure)?;
    toasty::create!(AuthFactor {
        user_id: user_id.to_string(),
        panel,
        kind,
        secret,
        confirmed_at: None,
        last_step: None,
        failures: 0,
        retry_at: None,
        created_at: Timestamp::now(),
    })
    .exec(ex)
    .await
    .map_err(infrastructure_failure)?;
    Ok(())
}

/// Starts setting up an authenticator for `user_id`: a new secret, sealed. Answers the secret,
/// for the QR code.
async fn start_authenticator(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    user_id: &str,
) -> topcoat::Result<Vec<u8>> {
    let secret = totp::secret();
    let sealed = cipher::seal(key(cx)?, &secret, &binding(user_id, &panel_prefix(cx)));
    start(cx, ex, user_id, FactorKind::Authenticator, sealed).await?;
    Ok(secret.to_vec())
}

/// The secret `factor` seals, or `None` when the router's key no longer opens it.
fn secret(cx: &Cx, factor: &AuthFactor) -> topcoat::Result<Option<Vec<u8>>> {
    Ok(cipher::open(
        key(cx)?,
        &factor.secret,
        &binding(&factor.user_id, &factor.panel),
    ))
}

/// Whether `code` is the current code of `factor`'s authenticator, not used before; a match
/// records its step through `ex`, so the code works once.
async fn accept_code(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    factor: &AuthFactor,
    code: &str,
) -> topcoat::Result<bool> {
    let Some(secret) = secret(cx, factor)? else {
        tracing::error!(panel = %factor.panel, "a two-factor secret does not open under the key");
        return Ok(false);
    };
    let now = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map_err(|_| crate::error::declaration("the clock is before 1970"))?
        .as_secs();
    let used = factor.last_step.and_then(|step| u64::try_from(step).ok());
    let Some(step) = totp::verify(&secret, code, totp::step(now), used) else {
        return Ok(false);
    };
    AuthFactor::filter(AuthFactor::fields().id().eq(factor.id))
        .update()
        .last_step(i64::try_from(step).ok())
        .exec(ex)
        .await
        .map_err(infrastructure_failure)?;
    Ok(true)
}

/// A recovery code as typed, read the way it was issued: lowercase, without separators.
fn normalize_recovery_code(code: &str) -> String {
    code.chars()
        .filter(char::is_ascii_alphanumeric)
        .map(|c| c.to_ascii_lowercase())
        .collect()
}

/// A recovery code as `user_id`'s row on `panel` stores it: keyed under the router's cookie key.
fn recovery_hash(cx: &Cx, user_id: &str, panel: &str, code: &str) -> topcoat::Result<String> {
    Ok(cipher::recovery_hash(
        key(cx)?,
        &binding(user_id, panel),
        &normalize_recovery_code(code),
    ))
}

/// Whether `code` is one of `user_id`'s recovery codes on the request's panel; a match is deleted
/// through `ex`, so each works once.
async fn spend_recovery_code(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    user_id: &str,
    code: &str,
) -> topcoat::Result<bool> {
    let panel = panel_prefix(cx);
    let hash = recovery_hash(cx, user_id, &panel, code)?;
    let codes = factors(&mut *ex, &panel, user_id).await?;
    let Some(matched) = codes.iter().find(|factor| {
        factor.kind == FactorKind::RecoveryCode
            && bool::from(factor.secret.as_bytes().ct_eq(hash.as_bytes()))
    }) else {
        return Ok(false);
    };
    AuthFactor::filter(AuthFactor::fields().id().eq(matched.id))
        .delete()
        .exec(ex)
        .await
        .map_err(infrastructure_failure)?;
    Ok(true)
}

/// Whether `code` is a code of `factor`, used up: its authenticator's current one, or the one
/// last mailed for it.
async fn accept_factor(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    factor: &AuthFactor,
    code: &str,
) -> topcoat::Result<bool> {
    match factor.kind {
        FactorKind::Authenticator => accept_code(cx, ex, factor, code).await,
        FactorKind::EmailCode => email::accept(cx, ex, &factor.user_id, code).await,
        FactorKind::RecoveryCode => Ok(false),
    }
}

/// Whether `code` reads as a code of the factor rather than a recovery code: apps show a code as
/// "123 456"; a recovery code is ten characters, so six digits are a code.
fn factor_code(code: &str) -> Option<String> {
    let code: String = code.chars().filter(|c| !c.is_whitespace()).collect();
    (code.len() == 6 && code.bytes().all(|b| b.is_ascii_digit())).then_some(code)
}

/// Whether `code` proves `user_id` holds their second factor on the request's panel: a code of
/// their confirmed factor, or one of their recovery codes, which it uses up.
pub(super) async fn accept(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    user_id: &str,
    code: &str,
) -> topcoat::Result<bool> {
    let enrolment = enrolment(cx, &mut *ex, user_id).await?;
    let Some(factor) = enrolment.confirmed else {
        return Ok(false);
    };
    match factor_code(code) {
        Some(code) => accept_factor(cx, ex, &factor, &code).await,
        None => {
            let code: String = code.chars().filter(|c| !c.is_whitespace()).collect();
            spend_recovery_code(cx, ex, user_id, &code).await
        }
    }
}

/// Fresh recovery codes for `user_id` on the request's panel, in place of any earlier ones.
/// Answers the codes, which are shown once: only their hashes are stored.
async fn issue_recovery_codes(
    cx: &Cx,
    ex: &mut dyn toasty::Executor,
    user_id: &str,
) -> topcoat::Result<Vec<String>> {
    let panel = panel_prefix(cx);
    AuthFactor::filter(
        AuthFactor::fields()
            .user_id()
            .eq(user_id.to_string())
            .and(AuthFactor::fields().panel().eq(panel.clone()))
            .and(AuthFactor::fields().kind().eq(FactorKind::RecoveryCode)),
    )
    .delete()
    .exec(&mut *ex)
    .await
    .map_err(infrastructure_failure)?;
    let mut codes = Vec::with_capacity(RECOVERY_CODES);
    let now = Timestamp::now();
    for _ in 0..RECOVERY_CODES {
        let code = recovery_code();
        toasty::create!(AuthFactor {
            user_id: user_id.to_string(),
            panel: panel.clone(),
            kind: FactorKind::RecoveryCode,
            secret: recovery_hash(cx, user_id, &panel, &code)?,
            confirmed_at: Some(now),
            last_step: None,
            failures: 0,
            retry_at: None,
            created_at: now,
        })
        .exec(&mut *ex)
        .await
        .map_err(infrastructure_failure)?;
        codes.push(code);
    }
    Ok(codes)
}

/// A random recovery code: ten characters of [`RECOVERY_ALPHABET`], in two groups of five.
fn recovery_code() -> String {
    let mut bytes = [0u8; 10];
    getrandom::fill(&mut bytes).expect("the recovery code randomness source failed");
    // 256 is a multiple of 32, so the low five bits are uniform.
    let chars: String = bytes
        .iter()
        .map(|byte| char::from(RECOVERY_ALPHABET[usize::from(byte & 31)]))
        .collect();
    format!("{}-{}", &chars[..5], &chars[5..])
}

/// Deletes every factor `user_id` holds on the request's panel, through `ex`.
async fn remove_all(cx: &Cx, ex: &mut dyn toasty::Executor, user_id: &str) -> topcoat::Result<()> {
    AuthFactor::filter(
        AuthFactor::fields()
            .user_id()
            .eq(user_id.to_string())
            .and(AuthFactor::fields().panel().eq(panel_prefix(cx))),
    )
    .delete()
    .exec(ex)
    .await
    .map_err(infrastructure_failure)
}

/// The mistakes in a panel's [`Auth::two_factor`](super::Auth::two_factor): two-factor sign-in
/// without auth, and a router without the cookie key that seals the secrets.
pub(super) fn declaration_errors(
    auth: &super::AuthConfig,
    has_key: bool,
) -> Vec<crate::DeclarationErrorKind> {
    use crate::{DeclarationErrorKind, declaration::TwoFactorFault};

    if auth.two_factor.is_none() {
        return Vec::new();
    }
    if auth.authenticator().is_none() {
        return vec![DeclarationErrorKind::TwoFactor(
            TwoFactorFault::AuthDisabled,
        )];
    }
    if has_key {
        Vec::new()
    } else {
        vec![DeclarationErrorKind::TwoFactor(TwoFactorFault::MissingKey)]
    }
}

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

    /// A recovery code reads the same however it is typed, and two codes differ.
    #[test]
    fn a_recovery_code_matches_however_it_is_typed() {
        let code = recovery_code();
        assert_eq!(code.len(), 11);
        let read = normalize_recovery_code(&code);
        assert_eq!(normalize_recovery_code(&code.to_uppercase()), read);
        assert_eq!(normalize_recovery_code(&code.replace('-', " ")), read);
        assert_ne!(normalize_recovery_code(&recovery_code()), read);
    }
}