// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Commercial
// SPDX-FileCopyrightText: 2025-2026 Christian Galo

package auth

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"database/sql"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"net/url"
	"slices"
	"strings"
	"time"

	"git.coopcloud.tech/wiki-cafe/member-console/internal/config"
	"git.coopcloud.tech/wiki-cafe/member-console/internal/identity"
	"git.coopcloud.tech/wiki-cafe/member-console/internal/logging"
	"git.coopcloud.tech/wiki-cafe/member-console/internal/organization"
	"git.coopcloud.tech/wiki-cafe/member-console/internal/provisioning"

	"github.com/alexedwards/scs/redisstore"
	"github.com/alexedwards/scs/v2"
	"github.com/coreos/go-oidc/v3/oidc"
	"github.com/gomodule/redigo/redis"
	"github.com/spf13/viper"
	"golang.org/x/oauth2"
	"golang.org/x/sync/singleflight"
)

// FailurePage renders the page a person lands on when an authentication flow
// refuses: a heading naming what failed, and the one link that leads out.
//
// The interface is declared here, and internal/server's template set
// satisfies it, because the server imports this package -- so this package
// cannot import the server to reach the renderer directly (design.md, D1).
type FailurePage interface {
	RenderAuthFailure(w http.ResponseWriter, r *http.Request, status int, heading, actionLabel, actionHref string)
}

// authFailure is what a person is told when a flow refuses. Every refusal in
// this package is reached by a browser following a redirect, so every one of
// them ends on a page rather than in plain text.
type authFailure struct {
	heading     string
	actionLabel string
	actionHref  string
}

// The four ways an authentication flow can dead-end. Each names what the
// person was doing and links back to the flow they were in, because the
// dashboard -- the ordinary error page's way out -- is the page they could
// not reach.
//
// Sign-in splits in two. The difference is the one thing the person cannot
// work out for themselves: whether trying again is likely to work. Expired
// is the flow going stale or being replayed, where a fresh attempt succeeds.
// Failed is the token exchange, the identity provider's answer, or this
// console's own provisioning breaking, where it may not; the log line says
// which.
//
// Sign-out refuses only when the provider's logout URL cannot be built or the
// store refuses to end the session; in both the person is still signed in, so
// retrying the sign-out is the honest way out. The retry is the account
// menu's Sign out (a POST), so the page's link leads back to the console.
var (
	signInExpired      = authFailure{"Sign-in expired", "Sign in again", "/login"}
	signInFailed       = authFailure{"Sign-in failed", "Sign in again", "/login"}
	registrationFailed = authFailure{"Registration failed", "Start again", "/register"}
	signOutFailed      = authFailure{"Sign-out failed", "Back to the console", "/"}
)

// retryableAuthorizationErrors are the identity provider's error codes that a
// fresh attempt clears: the provider was briefly unavailable, or it wants the
// person to interact with it again. Every other code names a configuration or
// authorization problem that a second attempt reproduces.
var retryableAuthorizationErrors = map[string]bool{
	// RFC 6749 section 4.1.2.1
	"temporarily_unavailable": true,
	"server_error":            true,
	// OIDC Core section 3.1.2.6
	"login_required":             true,
	"interaction_required":       true,
	"consent_required":           true,
	"account_selection_required": true,
}

// authorizationFailure chooses what a person is told about an error the
// identity provider returned, on the one axis they can act on.
func authorizationFailure(code string) authFailure {
	if retryableAuthorizationErrors[code] {
		return signInExpired
	}
	return signInFailed
}

// Config holds all auth-related configuration
type Config struct {
	SessionManager *scs.SessionManager
	OAuthConfig    *oauth2.Config
	Verifier       *oidc.IDTokenVerifier
	Provider       *oidc.Provider
	Database       *sql.DB              // Raw DB for transactions (auto-provisioning)
	IdentityQ      identity.Querier     // Identity module queries
	OrgQ           organization.Querier // Organization module queries

	// Failures renders a refused flow. The server assigns it once the
	// template set exists. A Config built without one (every test in this
	// package) answers with plain text, so a refusal is never a nil
	// dereference.
	Failures FailurePage

	// EndSessionEndpoint is the provider's RP-initiated logout endpoint
	// (OpenID Connect RP-Initiated Logout 1.0, section 2.1), read from
	// discovery at Setup. A provider that publishes none cannot end its
	// session on the person's behalf, and Setup refuses to start rather
	// than guess a path.
	EndSessionEndpoint string

	// RevocationEndpoint is the provider's token revocation endpoint (RFC
	// 7009), read from discovery at Setup. Empty when the provider
	// publishes none; the refresh token is then not revoked at sign-out,
	// which Setup says once at boot.
	RevocationEndpoint string

	// refreshes serialises identity re-derivation per session, keyed by
	// session token (refreshIdentity). Its zero value is ready to use.
	refreshes singleflight.Group
}

// providerEndpoints reads the endpoints sign-out needs beyond the OAuth 2.0
// pair from the provider's discovery document.
func providerEndpoints(provider *oidc.Provider) (endSession, revocation string, err error) {
	var meta struct {
		EndSessionEndpoint string `json:"end_session_endpoint"`
		RevocationEndpoint string `json:"revocation_endpoint"`
	}
	if err := provider.Claims(&meta); err != nil {
		return "", "", fmt.Errorf("reading the identity provider's discovery document: %w", err)
	}
	if meta.EndSessionEndpoint == "" {
		return "", "", errors.New("the identity provider publishes no end_session_endpoint; sign-out needs OpenID Connect RP-Initiated Logout 1.0")
	}
	return meta.EndSessionEndpoint, meta.RevocationEndpoint, nil
}

// showFailure answers a refused authentication flow with the styled page, or
// with the heading as plain text when no renderer is wired.
func (c *Config) showFailure(w http.ResponseWriter, r *http.Request, status int, f authFailure) {
	if c.Failures != nil {
		c.Failures.RenderAuthFailure(w, r, status, f.heading, f.actionLabel, f.actionHref)
		return
	}
	http.Error(w, f.heading, status)
}

// Setup initializes the auth configuration
func Setup(database *sql.DB, identityQ identity.Querier, orgQ organization.Querier) (*Config, error) {
	ctx := context.Background()
	logger := logging.FromContext(ctx)

	// Create Redis pool for Valkey
	dialOptions := valkeyDialOptions(ctx)
	pool := &redis.Pool{
		MaxIdle:     10,
		IdleTimeout: 240 * time.Second,
		Dial: func() (redis.Conn, error) {
			return redis.Dial("tcp", viper.GetString("valkey-addr"), dialOptions...)
		},
		TestOnBorrow: func(c redis.Conn, t time.Time) error {
			if time.Since(t) < time.Minute {
				return nil
			}
			_, err := c.Do("PING")
			return err
		},
	}

	// Test connection
	conn := pool.Get()
	defer conn.Close()
	if _, err := conn.Do("PING"); err != nil {
		return nil, fmt.Errorf("failed to connect to Valkey: %w", err)
	}
	logger.Info("session store connected",
		slog.String("addr", viper.GetString("valkey-addr")))

	sessionManager := newSessionManager(redisstore.New(pool))

	// Initialize OIDC provider
	provider, err := oidc.NewProvider(ctx, viper.GetString("oidc-idp-issuer-url"))
	if err != nil {
		return nil, fmt.Errorf("failed to initialize OIDC provider: %w", err)
	}
	endSession, revocation, err := providerEndpoints(provider)
	if err != nil {
		return nil, err
	}
	if revocation == "" {
		logger.Warn("the identity provider publishes no revocation_endpoint; refresh tokens will not be revoked at sign-out")
	}

	// Create OAuth2 config
	oauthConfig := &oauth2.Config{
		ClientID:     viper.GetString("oidc-sp-client-id"),
		ClientSecret: viper.GetString("oidc-sp-client-secret"),
		RedirectURL:  viper.GetString("base-url") + "/callback",
		Endpoint:     provider.Endpoint(),
		Scopes:       []string{oidc.ScopeOpenID, "profile", "email"},
	}

	// Create auth config
	config := &Config{
		SessionManager: sessionManager,
		OAuthConfig:    oauthConfig,
		Provider:       provider,
		Verifier:       provider.Verifier(&oidc.Config{ClientID: oauthConfig.ClientID}),
		Database:       database,
		IdentityQ:      identityQ,
		OrgQ:           orgQ,

		EndSessionEndpoint: endSession,
		RevocationEndpoint: revocation,
	}

	return config, nil
}

// newSessionManager builds the session manager over store.
//
// The cookie is Secure exactly when base-url is https (config.ServesHTTPS):
// that is the transport the browser sees, and the flag tells the browser to
// send the cookie over nothing less. Until the 2026-09 security audit
// (finding 5, decision D3) the flag followed the env key being exactly
// "production", so any other label, the default included, shipped the session
// cookie over plain HTTP wherever a plain-HTTP path existed.
func newSessionManager(store scs.Store) *scs.SessionManager {
	sessionManager := scs.New()
	sessionManager.Store = store
	sessionManager.Lifetime = 7 * 24 * time.Hour // 1 week
	sessionManager.Cookie.Name = "session"
	sessionManager.Cookie.Path = "/"
	sessionManager.Cookie.HttpOnly = true
	sessionManager.Cookie.Secure = config.ServesHTTPS()
	sessionManager.Cookie.SameSite = http.SameSiteLaxMode
	return sessionManager
}

// RegisterHandlers adds all auth-related handlers to the router
func (c *Config) RegisterHandlers(mux *http.ServeMux) {
	mux.HandleFunc("/login", c.LoginHandler)
	mux.HandleFunc("/callback", c.CallbackHandler)
	mux.HandleFunc("POST /logout", c.LogoutHandler)
	mux.HandleFunc("GET /logout", c.logoutGet)
	mux.HandleFunc("/logout-callback", c.LogoutCallbackHandler)
	mux.HandleFunc("/register", c.RegistrationHandler)
}

// Middleware returns an auth middleware function. selfAuthenticatedPaths
// are integration-declared endpoints that verify their own caller (provider
// webhooks checking an HMAC signature) — they must bypass session auth or
// the provider's delivery bounces off the /login redirect. The server
// passes the paths collected from RouteMount.CSRFExemptPaths: a path that
// authenticates by signature is exempt from both protections for the same
// reason.
func (c *Config) Middleware(selfAuthenticatedPaths ...string) func(http.Handler) http.Handler {
	publicPaths := map[string]bool{
		"/login":           true,
		"/callback":        true,
		"/logout":          true,
		"/logout-callback": true,
		"/register":        true,
		"/favicon.ico":     true, // Browser-fired in parallel with page loads; must not bounce through /login
	}
	for _, p := range selfAuthenticatedPaths {
		publicPaths[p] = true
	}
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if publicPaths[r.URL.Path] {
				next.ServeHTTP(w, r)
				return
			}

			// Skip authentication for static assets (public, no session needed)
			if strings.HasPrefix(r.URL.Path, "/static/") {
				next.ServeHTTP(w, r)
				return
			}

			// Check if authenticated
			if !c.SessionManager.GetBool(r.Context(), sessionKeyAuthenticated) {
				c.bounceToLogin(w, r)
				return
			}

			// An authenticated session can outlive the person it names:
			// the row behind the session's person id is gone after an
			// identity merge or purge, or after the database was rebuilt
			// from a snapshot (the demo reset). Every write such a session
			// makes then attributes itself to a person that does not
			// exist and fails on a foreign key deep in a handler
			// (fk_grants_granted_by_person_id on a ladder reorder,
			// 2026-09-03) instead of at sign-in. So the person is looked
			// up on every authenticated request (one primary-key read,
			// static assets excluded above); a session whose person is
			// gone ends here and the request bounces to /login exactly as
			// an unauthenticated one does.
			if !c.sessionPersonExists(r.Context()) {
				c.endSession(r.Context())
				c.bounceToLogin(w, r)
				return
			}

			// The identity provider is asked, once per interval, whether
			// this session's person is still who they were with the roles
			// they had (refreshIdentity). A definitive no ends the session
			// here, exactly as a missing person does.
			if !c.refreshIdentity(r.Context()) {
				c.endSession(r.Context())
				c.bounceToLogin(w, r)
				return
			}

			next.ServeHTTP(w, r)
		})
	}
}

// bounceToLogin sends a request that has no usable session to /login.
//
// Where the request was headed is remembered first so CallbackHandler can
// send the person back there after sign-in instead of always landing on
// "/" (ACC-9, design D2). Only a same-origin relative path from a GET
// request is safe to store: a POST's target is not a page to land on, and
// an HTMX request's own URL is a fetch endpoint (a partial), not a page
// either — its same-origin Referer, the document that made the fetch, is
// recorded instead. The value rides in the ordinary session (the same
// store LoginHandler's state/nonce/codeVerifier use), so it survives the
// five-minute pending-flow reuse window untouched.
//
// An HTMX request can't follow a 302 to the cross-origin Keycloak
// authorize URL — the XHR fails with status 0 and error-handler.js shows a
// misleading "Network error" toast with no way back to /login (finding
// #15). Such a request gets a 401 with HX-Redirect so htmx performs a
// same-origin client-side redirect to /login instead, matching the
// HX-Request convention used elsewhere (billing.go, operator.go). A page
// load gets the plain 302.
func (c *Config) bounceToLogin(w http.ResponseWriter, r *http.Request) {
	// The default return path ("/") carries no information CallbackHandler's
	// fallback doesn't already give it, so storing it bought nothing but a
	// session-store write and a seven-day cookie on every anonymous request
	// (design D3). A bare request that would only store "/" now modifies
	// nothing, and scs writes nothing to the store or the response.
	if r.Method == http.MethodGet {
		if r.Header.Get("HX-Request") == "true" {
			if dest, ok := sameOriginReturnTo(r.Referer(), r); ok && dest != "/" {
				c.SessionManager.Put(r.Context(), sessionKeyReturnTo, dest)
			}
		} else if dest, ok := validReturnTo(r.URL.RequestURI()); ok && dest != "/" {
			c.SessionManager.Put(r.Context(), sessionKeyReturnTo, dest)
		}
	}

	w.Header().Add("Vary", "HX-Request")
	if r.Header.Get("HX-Request") == "true" {
		w.Header().Set("HX-Redirect", "/login")
		w.WriteHeader(http.StatusUnauthorized)
		return
	}
	http.Redirect(w, r, "/login", http.StatusFound)
}

// sessionPersonExists reports whether the person an authenticated session
// names still has a row. Two answers count as gone: a definite "no such
// row" from the lookup (sql.ErrNoRows, what a sqlc :one query returns), and
// an authenticated session with no person id at all. Any other lookup
// error is logged and treated as "cannot tell", and the request proceeds:
// the handler reads the same database and fails on its own terms, and a
// blip must not sign everyone out. A Config built without IdentityQ (tests
// build one by hand; Setup always wires it) cannot look anyone up and
// proceeds the same way.
func (c *Config) sessionPersonExists(ctx context.Context) bool {
	personID := c.SessionManager.GetString(ctx, sessionKeyPersonID)
	if personID == "" {
		logging.FromContext(ctx).Warn("authenticated session names no person; ending the session")
		return false
	}
	if c.IdentityQ == nil {
		return true
	}
	_, err := c.IdentityQ.GetPersonByID(ctx, personID)
	switch {
	case err == nil:
		return true
	case errors.Is(err, sql.ErrNoRows):
		logging.FromContext(ctx).Warn("person behind an authenticated session no longer exists; ending the session",
			slog.String("person_id", personID))
		return false
	default:
		logging.FromContext(ctx).Warn("could not verify the person behind the session; letting the request through",
			slog.String("person_id", personID),
			slog.Any("error", err))
		return true
	}
}

// endSession drops everything the session holds and retires its token, so
// the cookie the browser still carries names a session that no longer
// exists in the store: Clear, then RenewToken, which deletes the old token
// and issues a new, empty one (bounceToLogin may still record a return-to
// in it). If the store refuses either step, Destroy is the fallback; it
// deletes the token and expires the cookie outright.
func (c *Config) endSession(ctx context.Context) {
	if err := c.SessionManager.Clear(ctx); err == nil {
		if err := c.SessionManager.RenewToken(ctx); err == nil {
			return
		}
	}
	if err := c.SessionManager.Destroy(ctx); err != nil {
		logging.FromContext(ctx).Error("could not end the session",
			slog.Any("error", err))
	}
}

// LoginHandler initiates the OIDC authentication flow
func (c *Config) LoginHandler(w http.ResponseWriter, r *http.Request) {
	// Rotate the session token before writing OIDC flow data.
	//
	// Defends against two things:
	//   1. Session fixation (OAuth 2.1 BCP §4.5 — start every authn from a
	//      fresh session ID).
	//   2. Stale browser cookies pointing at a session that no longer exists
	//      in the store (e.g. after a Valkey teardown). Without this, scs
	//      silently creates an empty session on the store miss, /login writes
	//      state into it, but the browser keeps sending the original cookie
	//      to /callback — savedState comes back empty and the user is stuck.
	//      RenewToken issues a new session ID and Set-Cookie on the redirect
	//      to the IdP, guaranteeing the cookie that returns to /callback maps
	//      to the session we just wrote state into.
	if err := c.SessionManager.RenewToken(r.Context()); err != nil {
		logging.FromContext(r.Context()).Error("sign-in could not renew the session token",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
		return
	}

	// Reuse a pending, recent OIDC flow instead of overwriting it. Parallel
	// /login hits in one session (a page load fanning out into a favicon
	// fetch, or a second tab) each used to generate fresh state and clobber
	// the other's; the IdP then returned a state the session no longer held,
	// producing "State mismatch" 400s at /callback. The state stays
	// single-use (CallbackHandler clears it on success) and a stale flow is
	// replaced wholesale.
	state := c.SessionManager.GetString(r.Context(), sessionKeyState)
	nonce := c.SessionManager.GetString(r.Context(), sessionKeyNonce)
	codeVerifier := c.SessionManager.GetString(r.Context(), sessionKeyCodeVerifier)
	issuedAt := c.SessionManager.GetInt64(r.Context(), sessionKeyStateIssuedAt)
	reusable := state != "" && nonce != "" && codeVerifier != "" &&
		issuedAt > 0 && time.Since(time.Unix(issuedAt, 0)) < loginStateReuseWindow
	if !reusable {
		state = generateRandomString(32)
		nonce = generateRandomString(32)
		codeVerifier = generateRandomString(32)

		// Store OIDC flow data in session
		c.SessionManager.Put(r.Context(), sessionKeyState, state)
		c.SessionManager.Put(r.Context(), sessionKeyNonce, nonce)
		c.SessionManager.Put(r.Context(), sessionKeyCodeVerifier, codeVerifier)
		c.SessionManager.Put(r.Context(), sessionKeyStateIssuedAt, time.Now().Unix())
	}
	// A session /login writes to lives only long enough to be worth
	// attacking: the five-minute state freshness window (loginStateReuseWindow)
	// plus headroom for a second factor at the provider (design D3). A
	// successful callback restores the full lifetime; one that never
	// completes leaves nothing behind past this deadline. Set on the reuse
	// path too, so a second /login hit within the window extends the
	// deadline exactly as it extends the flow's freshness.
	c.SessionManager.SetDeadline(r.Context(), time.Now().Add(loginSessionDeadline))
	hashVal := sha256.Sum256([]byte(codeVerifier))
	codeChallenge := base64.RawURLEncoding.EncodeToString(hashVal[:])

	authURL := c.OAuthConfig.AuthCodeURL(
		state,
		oidc.Nonce(nonce),
		oauth2.SetAuthURLParam("code_challenge", codeChallenge),
		oauth2.SetAuthURLParam("code_challenge_method", "S256"),
	)
	http.Redirect(w, r, authURL, http.StatusFound)
}

// CallbackHandler processes the OIDC callback
func (c *Config) CallbackHandler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	logger := logging.FromContext(ctx)

	// Validate state.
	//
	// A genuine mismatch (savedState present but different) stays a hard 400 —
	// it's a CSRF/replay signal. But savedState == "" means the session we
	// wrote state into at /login is gone by the time the IdP redirected back
	// (lost cookie, expired session, store wiped). That's a UX failure, not an
	// attack: send the user back through /login so they get a fresh session
	// and try once more transparently.
	state := r.URL.Query().Get("state")
	savedState := c.SessionManager.GetString(ctx, sessionKeyState)
	if savedState == "" {
		logger.Info("callback has no saved state; restarting sign-in")
		http.Redirect(w, r, "/login", http.StatusFound)
		return
	}
	if state != savedState {
		// %q escapes newlines and control characters, so a crafted state
		// cannot forge additional log records. The saved state is not logged:
		// it is a CSRF-grade secret and a mismatch is diagnostic on its own.
		logger.Warn("callback state does not match the session",
			slog.String("state", state))
		c.showFailure(w, r, http.StatusBadRequest, signInExpired)
		return
	}

	// The identity provider may answer the authorization request with an
	// error instead of a code (RFC 6749 section 4.1.2.1, OIDC Core section
	// 3.1.2.6). The console used to ignore the parameter and carry on to the
	// token exchange with an empty code, which failed as an internal error
	// and told the person nothing about what had actually happened. That is
	// the shape a Keycloak page left open long enough to answer
	// "temporarily_unavailable / authentication_expired" comes back in;
	// reproduced live on 2026-09-08.
	//
	// The state is validated above first, deliberately: an error response
	// carries the state too, so an unsolicited one must not be able to end a
	// flow the person is still in.
	if authErr := r.URL.Query().Get("error"); authErr != "" {
		logger.Warn("the identity provider refused the authorization request",
			slog.String("error", authErr),
			slog.String("error_description", r.URL.Query().Get("error_description")))
		c.showFailure(w, r, http.StatusBadRequest, authorizationFailure(authErr))
		return
	}

	// Exchange code
	code := r.URL.Query().Get("code")
	codeVerifier := c.SessionManager.GetString(ctx, sessionKeyCodeVerifier)
	if codeVerifier == "" {
		logger.Warn("callback has no code verifier in the session")
		c.showFailure(w, r, http.StatusBadRequest, signInExpired)
		return
	}

	token, err := c.OAuthConfig.Exchange(
		ctx,
		code,
		oauth2.VerifierOption(codeVerifier),
	)
	if err != nil {
		logger.Error("token exchange failed",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
		return
	}

	// Verify ID token
	rawIDToken, ok := token.Extra("id_token").(string)
	if !ok {
		logger.Error("token response carries no ID token")
		c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
		return
	}

	idToken, err := c.Verifier.Verify(ctx, rawIDToken)
	if err != nil {
		logger.Warn("ID token failed verification",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
		return
	}

	// Verify nonce
	var nonceClaims struct {
		Nonce string `json:"nonce"`
	}
	if err := idToken.Claims(&nonceClaims); err != nil {
		logger.Error("could not parse the ID token's nonce claim",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
		return
	}

	savedNonce := c.SessionManager.GetString(ctx, sessionKeyNonce)
	if nonceClaims.Nonce != savedNonce {
		logger.Warn("ID token nonce does not match the session")
		c.showFailure(w, r, http.StatusBadRequest, signInExpired)
		return
	}

	// ---- Database Interaction & User Info Extraction ----
	var userInfoClaims struct {
		Subject           string `json:"sub"`
		Email             string `json:"email"`
		EmailVerified     bool   `json:"email_verified"`
		Name              string `json:"name"`
		PreferredUsername string `json:"preferred_username"`
		GivenName         string `json:"given_name"`
		FamilyName        string `json:"family_name"`
	}
	if err := idToken.Claims(&userInfoClaims); err != nil {
		logger.Error("could not parse the ID token's user claims",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
		return
	}

	// Session variables to populate
	var personID, orgID, workspaceID string

	user, err := c.IdentityQ.GetUserByOIDCSubject(ctx, userInfoClaims.Subject)
	if err != nil {
		if err == sql.ErrNoRows {
			// New user — auto-provision all governance structures
			result, errProv := provisioning.AutoProvision(ctx, c.Database, provisioning.OIDCClaims{
				Subject:           userInfoClaims.Subject,
				Email:             userInfoClaims.Email,
				EmailVerified:     userInfoClaims.EmailVerified,
				Name:              userInfoClaims.Name,
				PreferredUsername: userInfoClaims.PreferredUsername,
			})
			if errProv != nil {
				logger.Error("auto-provisioning a new person failed",
					slog.Any("error", errProv))
				c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
				return
			}
			user = result.User
			personID = result.Person.PersonID
			orgID = result.Org.OrgID
			workspaceID = result.Workspace.WorkspaceID
			logger.Info("new person provisioned at sign-in",
				slog.String("email", userInfoClaims.Email),
				slog.String("person_id", personID),
				slog.String("org_id", orgID))
		} else {
			logger.Error("could not look up the user by OIDC subject",
				slog.String("oidc_subject", userInfoClaims.Subject),
				slog.Any("error", err))
			c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
			return
		}
	} else {
		// Returning user — load existing governance records and update login
		_, errLogin := c.IdentityQ.UpdateUserLogin(ctx, identity.UpdateUserLoginParams{
			LastLoginAt: sql.NullTime{Time: time.Now(), Valid: true},
			LastLoginIp: sql.NullString{String: r.RemoteAddr, Valid: true},
			UserID:      user.UserID,
		})
		if errLogin != nil {
			logger.Warn("could not record the login timestamp",
				slog.String("user_id", user.UserID),
				slog.Any("error", errLogin))
		}

		// Load person
		person, errPerson := c.IdentityQ.GetPersonByUserID(ctx, user.UserID)
		if errPerson != nil {
			logger.Error("could not load the person behind the user",
				slog.String("user_id", user.UserID),
				slog.Any("error", errPerson))
			c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
			return
		}
		personID = person.PersonID

		// Update person if OIDC claims changed. The display name falls back
		// exactly as first-login provisioning does (name, then
		// preferred_username), and never to an empty string: an IdP that
		// omits `name` used to overwrite a good display name with "" here
		// (status/issues.md, "Returning-login resync overwrites...").
		resyncName := provisioning.DisplayNameFromClaims(userInfoClaims.Name, userInfoClaims.PreferredUsername)
		if resyncName == "" {
			resyncName = person.DisplayName
		}
		if person.DisplayName != resyncName || person.PrimaryEmail != userInfoClaims.Email {
			_, errUpdate := c.IdentityQ.UpdatePerson(ctx, identity.UpdatePersonParams{
				DisplayName:          resyncName,
				PrimaryEmail:         userInfoClaims.Email,
				PrimaryEmailVerified: userInfoClaims.EmailVerified,
				PersonID:             person.PersonID,
			})
			if errUpdate != nil {
				logger.Warn("could not resync the person from the ID token claims",
					slog.String("person_id", person.PersonID),
					slog.Any("error", errUpdate))
			}
		}

		// Load personal org (first org owned by this person)
		orgs, errOrgs := c.OrgQ.GetOrganizationsByOwner(ctx, personID)
		if errOrgs != nil || len(orgs) == 0 {
			logger.Error("could not load an organization for the person",
				slog.String("person_id", personID),
				slog.Any("error", errOrgs))
			c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
			return
		}
		orgID = orgs[0].OrgID

		// Load default workspace
		workspaces, errWS := c.OrgQ.GetWorkspacesByOrgID(ctx, orgID)
		if errWS != nil || len(workspaces) == 0 {
			logger.Error("could not load a workspace for the organization",
				slog.String("org_id", orgID),
				slog.Any("error", errWS))
			c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
			return
		}
		workspaceID = workspaces[0].WorkspaceID

		logger.Info("returning person signed in",
			slog.String("email", userInfoClaims.Email),
			slog.String("person_id", personID),
			slog.String("org_id", orgID))
	}

	// ---- Extract roles from the verified ID token (IdP-agnostic) ----
	roles := rolesFromIDToken(ctx, idToken, c.OAuthConfig.ClientID, userInfoClaims.Email)
	logger.Info("roles read from the ID token",
		slog.String("email", userInfoClaims.Email),
		slog.Any("roles", roles))

	// Clear OIDC flow data and set authenticated session data
	c.SessionManager.Remove(ctx, sessionKeyState)
	c.SessionManager.Remove(ctx, sessionKeyNonce)
	c.SessionManager.Remove(ctx, sessionKeyCodeVerifier)
	c.SessionManager.Remove(ctx, sessionKeyStateIssuedAt)

	// Rotate the session token again, now that the state, nonce and PKCE
	// checks and the code exchange have all passed, and before the identity
	// is written (design D2). LoginHandler's rotation only defeats fixation
	// planted before /login; a session id fixed between /login and /callback
	// still bound the matching state and would otherwise carry the identity
	// this handler is about to write. scs's own guidance is to renew on a
	// privilege change, and this is that change; RenewToken keeps the
	// session data (the OIDC keys just cleared are already gone, nothing
	// else is lost) and issues a fresh token under which the identity below
	// is the first thing written.
	if err := c.SessionManager.RenewToken(ctx); err != nil {
		logger.Error("callback could not renew the session token",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signInFailed)
		return
	}
	// A pre-authentication session lives fifteen minutes (LoginHandler); a
	// successful sign-in restores the full configured lifetime (design D3).
	c.SessionManager.SetDeadline(ctx, time.Now().Add(c.SessionManager.Lifetime))

	c.SessionManager.Put(ctx, sessionKeyAuthenticated, true)
	c.SessionManager.Put(ctx, sessionKeyIDToken, rawIDToken)
	if token.RefreshToken != "" {
		c.SessionManager.Put(ctx, sessionKeyRefreshToken, token.RefreshToken)
	}
	c.SessionManager.Put(ctx, sessionKeyPersonID, personID)
	c.SessionManager.Put(ctx, sessionKeyOrgID, orgID)
	c.SessionManager.Put(ctx, sessionKeyWorkspaceID, workspaceID)
	c.SessionManager.Put(ctx, sessionKeyOIDCSubject, user.OidcSubject)
	c.SessionManager.Put(ctx, sessionKeyEmail, userInfoClaims.Email)
	c.SessionManager.Put(ctx, sessionKeyName, userInfoClaims.Name)
	c.SessionManager.Put(ctx, sessionKeyUsername, userInfoClaims.PreferredUsername)
	c.SessionManager.Put(ctx, sessionKeyRoles, roles)
	c.SessionManager.Put(ctx, sessionKeyIdentityRefreshedAt, time.Now().Unix())

	dest := c.resolveReturnTo(ctx)
	logger.Info("sign-in complete",
		slog.String("email", userInfoClaims.Email),
		slog.String("destination", dest))
	http.Redirect(w, r, dest, http.StatusFound)
}

// resolveReturnTo consumes the return-to path the middleware recorded
// before redirecting to /login (ACC-9), one-time and re-validated since it
// round-tripped through session storage: a value that fails validReturnTo
// (a foreign origin, or nothing stored — including a direct /login visit,
// which never sets the key) falls back to "/".
func (c *Config) resolveReturnTo(ctx context.Context) string {
	returnTo := c.SessionManager.GetString(ctx, sessionKeyReturnTo)
	c.SessionManager.Remove(ctx, sessionKeyReturnTo)
	if dest, ok := validReturnTo(returnTo); ok {
		return dest
	}
	return "/"
}

// providerCallTimeout bounds each call made to the identity provider outside
// the browser's own redirects: the sign-out hint refresh, the revocation, and
// the interval re-derivation of a session's identity. Each failure costs only
// its own effect, so no request waits longer than this per call.
const providerCallTimeout = 5 * time.Second

// LogoutHandler ends the session here, then sends the browser to the identity
// provider to end its own.
//
// Until the 2026-09 security audit (finding 11, decision D5) the session was
// destroyed only in LogoutCallbackHandler, once the identity provider had
// redirected back and a logout state had matched. A person who never completed
// that round trip -- who closed the tab at Keycloak's "Do you want to log
// out?" prompt -- kept a working session for the rest of its week. The session
// now ends before the redirect, unconditionally.
//
// The second (2026-09, run two) audit found a forged GET straight at
// /logout-callback could still end an unrelated, live session, because that
// handler acted on nothing but its own arrival. The state generated below,
// held in the logout_state cookie and echoed back by the provider, is what
// lets the callback tell a genuine round trip apart from that forgery (design
// D4; see LogoutCallbackHandler).
//
// The prompt is avoided where it can be. The provider skips confirmation when
// the request carries a valid id_token_hint, and the stored ID token is valid
// only for its first few minutes, so an aged session mints a fresh one from the
// refresh token first (idTokenHint). When that is not possible the hint is
// omitted and the provider asks, exactly as before; the console session is gone
// either way.
//
// The refresh token is then revoked at the provider (revokeRefreshToken), so
// that no copy of it -- in a backup of the session store, in a log nobody
// meant to keep -- can mint tokens after the person signed out.
func (c *Config) LogoutHandler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	logger := logging.FromContext(ctx)

	// Sign-out changes state, so it is a POST and the cross-origin
	// protection covers it: a page on another origin cannot end a person's
	// session by sending the browser here (2026-09 audit candidate "Logout
	// CSRF"). RegisterHandlers routes only POST here; the check stands for a
	// caller that wires the handler by hand.
	if r.Method != http.MethodPost {
		w.Header().Set("Allow", http.MethodPost)
		http.Error(w, http.StatusText(http.StatusMethodNotAllowed), http.StatusMethodNotAllowed)
		return
	}

	endSessionURL, err := url.Parse(c.EndSessionEndpoint)
	if err != nil || c.EndSessionEndpoint == "" {
		logger.Error("no usable end_session_endpoint; Setup guarantees one, so this Config was built by hand",
			slog.String("endpoint", c.EndSessionEndpoint),
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signOutFailed)
		return
	}

	// Everything the request needs from the session is read here, before
	// the session goes.
	storedRefreshToken := c.SessionManager.GetString(ctx, sessionKeyRefreshToken)
	hint, currentRefreshToken := c.idTokenHint(ctx, storedRefreshToken)

	// An unguessable state, echoed back to /logout-callback by the provider
	// (OpenID Connect RP-Initiated Logout 1.0, section 2), is what lets that
	// callback tell a genuine round trip from a forged visit once the
	// session it would have checked is already gone (design D4). It is held
	// in a cookie scoped to the callback path rather than the session, since
	// the session is destroyed below before the redirect; five minutes
	// covers the round trip to the provider and back.
	logoutState := generateRandomString(32)
	http.SetCookie(w, &http.Cookie{
		Name:     "logout_state",
		Value:    logoutState,
		Path:     "/logout-callback",
		HttpOnly: true,
		Secure:   config.ServesHTTPS(),
		SameSite: http.SameSiteLaxMode,
		MaxAge:   300,
	})

	q := endSessionURL.Query()
	q.Set("post_logout_redirect_uri", viper.GetString("base-url")+"/logout-callback")
	q.Set("client_id", viper.GetString("oidc-sp-client-id"))
	q.Set("state", logoutState)
	if hint != "" {
		q.Set("id_token_hint", hint)
	}
	endSessionURL.RawQuery = q.Encode()

	if err := c.SessionManager.Destroy(ctx); err != nil {
		logger.Error("could not end the session at sign-out",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, signOutFailed)
		return
	}

	c.revokeRefreshTokens(ctx, storedRefreshToken, currentRefreshToken)

	// Log the destination without its query string. The query carries
	// id_token_hint, a live token; logging the whole URL wrote it to the log
	// (2026-09 security audit). Redacting one named parameter would mean
	// keeping a list of secret parameter names in sync by hand; the
	// destination is the only part worth logging.
	loggableLogoutURL := *endSessionURL
	loggableLogoutURL.RawQuery = ""
	logger.Info("session ended; redirecting to the identity provider to sign out",
		slog.String("url", loggableLogoutURL.String()))
	// The account menu's Sign out is an htmx request, and fetch cannot
	// follow a redirect to another origin; HX-Redirect makes the browser
	// navigate to the provider instead. Anything else posting here gets the
	// redirect itself, 303 because the request was a POST (RFC 9110
	// section 15.4.4).
	w.Header().Add("Vary", "HX-Request")
	if r.Header.Get("HX-Request") == "true" {
		w.Header().Set("HX-Redirect", endSessionURL.String())
		w.WriteHeader(http.StatusOK)
		return
	}
	http.Redirect(w, r, endSessionURL.String(), http.StatusSeeOther)
}

// logoutGet answers a GET at /logout, which is never the account menu: it is
// an old bookmark, a typed address, or a link on some other page. None of
// those may end a session, so the browser is sent to the console's root,
// where the account menu is.
func (c *Config) logoutGet(w http.ResponseWriter, r *http.Request) {
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

// idTokenHint returns an ID token fit to send as id_token_hint, or "" when
// none can be had, together with the refresh token that is current afterwards.
//
// The stored token is used while it is still valid. Past that, a fresh one is
// minted from the refresh token: one call to the provider's token endpoint,
// bounded by providerCallTimeout. Its failure, or a provider that answers a
// refresh without an ID token (OIDC Core section 12.2 makes that optional),
// costs the hint and nothing else: the sign-out proceeds and the provider asks
// for confirmation, as it did before the refresh token was kept.
//
// A provider may rotate the refresh token on use (RFC 6749 section 6). The
// one returned is whichever is live afterwards, so the caller revokes the
// right one.
func (c *Config) idTokenHint(ctx context.Context, refreshToken string) (hint, currentRefreshToken string) {
	if stored := c.SessionManager.GetString(ctx, sessionKeyIDToken); stored != "" && idTokenUsableAsHint(stored, time.Now()) {
		return stored, refreshToken
	}
	if refreshToken == "" || c.OAuthConfig == nil {
		return "", refreshToken
	}

	logger := logging.FromContext(ctx)
	refreshCtx, cancel := context.WithTimeout(ctx, providerCallTimeout)
	defer cancel()
	// A token with no access token is not Valid, so the source refreshes on
	// the first call rather than returning what it was given.
	fresh, err := c.OAuthConfig.TokenSource(refreshCtx, &oauth2.Token{RefreshToken: refreshToken}).Token()
	if err != nil {
		logger.Warn("could not refresh the ID token for the sign-out hint; the identity provider will ask for confirmation",
			slog.Any("error", err))
		return "", refreshToken
	}
	if fresh.RefreshToken != "" {
		refreshToken = fresh.RefreshToken
	}
	idToken, _ := fresh.Extra("id_token").(string)
	if idToken == "" {
		logger.Warn("the identity provider's refresh response carries no ID token; the identity provider will ask for confirmation")
		return "", refreshToken
	}
	return idToken, refreshToken
}

// revokeRefreshTokens tells the identity provider the refresh tokens are no
// longer in use (RFC 7009, section 2.1). Best effort and bounded: a failure is
// logged at warning and costs nothing here, because the session that held the
// tokens is already gone and the provider's own logout, which the browser is
// about to request, invalidates the session's tokens as well.
//
// What it buys is the case where that logout does not happen -- no valid hint
// could be had and the person walked away from the confirmation page -- and,
// more generally, that a copy of the session store taken before sign-out
// holds a token that no longer works.
//
// Every token that was live is revoked: the stored one, and the one a refresh
// handed back when it differs. RFC 7009 obliges a provider to invalidate the
// token named and its access tokens, not other refresh tokens of the same
// grant, so a provider that hands out a new refresh token without retiring
// the old one would otherwise leave the old one working.
func (c *Config) revokeRefreshTokens(ctx context.Context, refreshTokens ...string) {
	if c.RevocationEndpoint == "" || c.OAuthConfig == nil {
		return
	}
	seen := map[string]bool{"": true}
	for _, token := range refreshTokens {
		if !seen[token] {
			seen[token] = true
			c.revokeRefreshToken(ctx, token)
		}
	}
}

// revokeRefreshToken is one revocation call. The client authenticates with
// HTTP Basic, the form RFC 6749 section 2.3.1 says a confidential client
// SHOULD use, with the id and secret form-encoded as that section requires. A
// provider answers 200 whether or not the token was live (RFC 7009 section
// 2.2), so anything else is worth a line.
func (c *Config) revokeRefreshToken(ctx context.Context, refreshToken string) {
	logger := logging.FromContext(ctx)

	revokeCtx, cancel := context.WithTimeout(ctx, providerCallTimeout)
	defer cancel()
	form := url.Values{"token": {refreshToken}, "token_type_hint": {"refresh_token"}}
	req, err := http.NewRequestWithContext(revokeCtx, http.MethodPost, c.RevocationEndpoint, strings.NewReader(form.Encode()))
	if err != nil {
		logger.Warn("could not build the refresh token revocation request",
			slog.Any("error", err))
		return
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.SetBasicAuth(url.QueryEscape(c.OAuthConfig.ClientID), url.QueryEscape(c.OAuthConfig.ClientSecret))

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		logger.Warn("could not revoke the refresh token at sign-out",
			slog.Any("error", err))
		return
	}
	defer resp.Body.Close()
	_, _ = io.Copy(io.Discard, resp.Body)
	if resp.StatusCode != http.StatusOK {
		logger.Warn("the identity provider did not accept the refresh token revocation",
			slog.Int("status", resp.StatusCode))
		return
	}
	logger.Debug("refresh token revoked at the identity provider")
}

// LogoutCallbackHandler is where the identity provider sends the browser once
// its own sign-out is done.
//
// The console session ended in LogoutHandler, so there is normally nothing
// here to verify. But the 2026-09 audit's second run found this handler
// acted on its own arrival alone: a forged GET straight at this path, from
// another origin, with no round trip through /logout at all, ended whatever
// session the browser happened to be carrying (design D4). The state
// LogoutHandler put in the logout_state cookie is what distinguishes the two:
// it lives only across a genuine round trip to the provider and back, scoped
// to this path, so a forged visit cannot present it. The comparison is
// constant-time because a state is exactly the kind of secret a timing
// side-channel could otherwise narrow down.
//
// A match ends whatever session the browser presents (normally none; the
// destroy at /logout already ran, but a store that refused that first
// delete, or a session that predates it, does not outlive this) and clears
// the cookie, landing on /login. Anything else -- no cookie, a state that
// does not match, no state at all -- leaves the session untouched: unlike a
// match, there is nothing here establishing the browser actually came from a
// sign-out this console started, and / is the page that knows whether to
// bounce a session that may still be live. The handler never refuses either
// way; it always redirects.
func (c *Config) LogoutCallbackHandler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	state := r.URL.Query().Get("state")
	cookieState := ""
	if cookie, err := r.Cookie("logout_state"); err == nil {
		cookieState = cookie.Value
	}
	matched := state != "" && cookieState != "" &&
		subtle.ConstantTimeCompare([]byte(state), []byte(cookieState)) == 1

	if !matched {
		http.Redirect(w, r, "/", http.StatusFound)
		return
	}

	if err := c.SessionManager.Destroy(ctx); err != nil {
		logging.FromContext(ctx).Warn("could not clear a session at the logout callback",
			slog.Any("error", err))
	}
	http.SetCookie(w, &http.Cookie{
		Name:     "logout_state",
		Value:    "",
		Path:     "/logout-callback",
		HttpOnly: true,
		Secure:   config.ServesHTTPS(),
		SameSite: http.SameSiteLaxMode,
		MaxAge:   -1,
	})
	http.Redirect(w, r, "/login", http.StatusFound)
}

// RegistrationHandler redirects to the OIDC registration page
func (c *Config) RegistrationHandler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	logger := logging.FromContext(ctx)

	// Rotate the session id before the flow starts, exactly as LoginHandler
	// does. Registration is the other path that ends in an authenticated
	// session, and it was the only one that did not rotate: a session id
	// planted in the browser beforehand survived the person's sign-in, which
	// is session fixation. Found by the 2026-09 security audit. This also
	// gives registration the same guarantee LoginHandler documents, that the
	// cookie returning to /callback maps to the session the state was written
	// into.
	if err := c.SessionManager.RenewToken(ctx); err != nil {
		logger.Error("registration could not renew the session token",
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, registrationFailed)
		return
	}

	state := generateRandomString(32)
	nonce := generateRandomString(32)
	codeVerifier := generateRandomString(32)
	hashVal := sha256.Sum256([]byte(codeVerifier))
	codeChallenge := base64.RawURLEncoding.EncodeToString(hashVal[:])

	c.SessionManager.Put(ctx, sessionKeyState, state)
	c.SessionManager.Put(ctx, sessionKeyNonce, nonce)
	c.SessionManager.Put(ctx, sessionKeyCodeVerifier, codeVerifier)

	registrationEndpoint := viper.GetString("oidc-idp-issuer-url") + "/protocol/openid-connect/registrations"

	parsedRegistrationURL, err := url.Parse(registrationEndpoint)
	if err != nil {
		logger.Error("could not build the identity provider's registration URL",
			slog.String("endpoint", registrationEndpoint),
			slog.Any("error", err))
		c.showFailure(w, r, http.StatusInternalServerError, registrationFailed)
		return
	}

	q := parsedRegistrationURL.Query()
	q.Set("client_id", viper.GetString("oidc-sp-client-id"))
	q.Set("response_type", "code")
	q.Set("scope", "openid email profile")
	q.Set("redirect_uri", viper.GetString("base-url")+"/callback")
	q.Set("state", state)
	q.Set("nonce", nonce)
	q.Set("code_challenge", codeChallenge)
	q.Set("code_challenge_method", "S256")

	parsedRegistrationURL.RawQuery = q.Encode()

	loggableRegistrationURL := *parsedRegistrationURL
	loggableRegistrationURL.RawQuery = ""
	logger.Info("redirecting to the identity provider to register",
		slog.String("url", loggableRegistrationURL.String()))
	http.Redirect(w, r, parsedRegistrationURL.String(), http.StatusFound)
}

// Identity re-derivation ------------------------------------------------------

// identityRefreshInterval bounds how long a change at the identity provider
// -- a role removed, an account disabled, a session ended by an administrator
// -- can go unnoticed by a signed-in session. Finding 3 of the 2026-09
// security audit (decision D2): roles were copied into the session at sign-in
// and read from that copy for the session's week-long life.
const identityRefreshInterval = 5 * time.Minute

// identityRefreshBackoff is how long a session waits before asking again
// after the provider gave no answer at all.
const identityRefreshBackoff = time.Minute

// identityRefresh is one answer from the provider, shared between requests
// that asked together.
type identityRefresh struct {
	idToken      string
	refreshToken string
	subject      string
	roles        []string
	refused      bool  // the provider said the grant is invalid: definitive
	err          error // no usable answer, or the definitive refusal's detail
}

// refreshIdentity re-derives a signed-in session's identity and roles from
// the identity provider once identityRefreshInterval has passed since the last
// time, and reports whether the session may continue.
//
// The question is put with the session's refresh token (OAuth 2.0 section 6),
// and the answer is a new ID token whose claims are current, so this needs
// nothing beyond what sign-in already needs: refresh tokens, and roles in the
// ID token. The answer is read the way sign-in read the original.
//
// Three outcomes. The provider refuses the grant (invalid_grant, RFC 6749
// section 5.2): the session is gone at the provider, the account is disabled,
// or the token was revoked, and the session ends now. The provider answers:
// roles, ID token and refresh token are replaced and the clock restarts. The
// provider gives no answer, a timeout, a 5xx, a verification failure: the
// session keeps its last known state and asks again after a short backoff,
// as the per-request person check treats a database blip. An outage at the
// provider must not sign everyone out, and a revoked operator cannot cause
// one.
//
// A session without a refresh token (a provider that issues none) stays on
// its sign-in snapshot for its lifetime, which is what every session did
// before this existed.
func (c *Config) refreshIdentity(ctx context.Context) bool {
	now := time.Now()
	if now.Unix()-c.SessionManager.GetInt64(ctx, sessionKeyIdentityRefreshedAt) < int64(identityRefreshInterval/time.Second) {
		return true
	}
	if c.SessionManager.GetInt64(ctx, sessionKeyIdentityRetryAt) > now.Unix() {
		return true
	}
	refreshToken := c.SessionManager.GetString(ctx, sessionKeyRefreshToken)
	if refreshToken == "" || c.OAuthConfig == nil || c.Verifier == nil {
		return true
	}
	logger := logging.FromContext(ctx)

	// One refresh per session at a time. Two requests crossing the interval
	// together would otherwise both present the same refresh token, and a
	// provider that retires a refresh token on use would refuse the second
	// as a replay, which reads as a definitive refusal below. Requests that
	// arrive while one is in flight share its answer.
	shared, _, _ := c.refreshes.Do(c.SessionManager.Token(ctx), func() (any, error) {
		return c.rederive(ctx, refreshToken), nil
	})
	answer := shared.(identityRefresh)

	switch {
	case answer.refused:
		logger.Warn("the identity provider refused the session's refresh token; ending the session",
			slog.Any("error", answer.err))
		return false
	case answer.err != nil:
		logger.Warn("could not re-derive the session's identity; keeping it and asking again later",
			slog.Any("error", answer.err))
		c.SessionManager.Put(ctx, sessionKeyIdentityRetryAt, now.Add(identityRefreshBackoff).Unix())
		return true
	}

	if subject := c.SessionManager.GetString(ctx, sessionKeyOIDCSubject); subject != "" && answer.subject != subject {
		logger.Error("the refreshed ID token names a different subject than the session; ending the session",
			slog.String("session_subject", subject),
			slog.String("token_subject", answer.subject))
		return false
	}

	before := c.getRoles(ctx)
	c.SessionManager.Put(ctx, sessionKeyIDToken, answer.idToken)
	if answer.refreshToken != "" {
		c.SessionManager.Put(ctx, sessionKeyRefreshToken, answer.refreshToken)
	}
	c.SessionManager.Put(ctx, sessionKeyRoles, answer.roles)
	c.SessionManager.Put(ctx, sessionKeyIdentityRefreshedAt, now.Unix())
	c.SessionManager.Remove(ctx, sessionKeyIdentityRetryAt)
	if !slices.Equal(before, answer.roles) {
		logger.Info("roles changed at the identity provider; session updated",
			slog.Any("before", before),
			slog.Any("after", answer.roles))
	}
	return true
}

// rederive is the one call to the provider: a refresh-token grant, the new ID
// token verified exactly as sign-in verifies one, and the roles read from it.
func (c *Config) rederive(ctx context.Context, refreshToken string) identityRefresh {
	callCtx, cancel := context.WithTimeout(ctx, providerCallTimeout)
	defer cancel()
	fresh, err := c.OAuthConfig.TokenSource(callCtx, &oauth2.Token{RefreshToken: refreshToken}).Token()
	if err != nil {
		var refusal *oauth2.RetrieveError
		if errors.As(err, &refusal) && refusal.ErrorCode == "invalid_grant" {
			return identityRefresh{refused: true, err: err}
		}
		return identityRefresh{err: err}
	}
	rawIDToken, _ := fresh.Extra("id_token").(string)
	if rawIDToken == "" {
		return identityRefresh{err: errors.New("the refresh response carries no ID token")}
	}
	idToken, err := c.Verifier.Verify(callCtx, rawIDToken)
	if err != nil {
		return identityRefresh{err: fmt.Errorf("verifying the refreshed ID token: %w", err)}
	}
	var claims struct {
		Email string `json:"email"`
	}
	_ = idToken.Claims(&claims)
	return identityRefresh{
		idToken:      rawIDToken,
		refreshToken: fresh.RefreshToken,
		subject:      idToken.Subject,
		roles:        rolesFromIDToken(ctx, idToken, c.OAuthConfig.ClientID, claims.Email),
	}
}

// Session key constants - single source of truth for session data
const (
	sessionKeyAuthenticated = "authenticated"
	sessionKeyIDToken       = "id_token"
	// The refresh token is kept for one purpose today: minting a fresh ID
	// token at sign-out so the identity provider gets a valid id_token_hint
	// and ends its session without asking for confirmation (LogoutHandler).
	// It lives only in the server-side store, never in the cookie.
	sessionKeyRefreshToken = "refresh_token"
	// Identity re-derivation (refreshIdentity): when the provider last
	// confirmed this session's identity and roles, and, after it gave no
	// answer, when to ask again.
	sessionKeyIdentityRefreshedAt = "identity_refreshed_at"
	sessionKeyIdentityRetryAt     = "identity_retry_at"
	sessionKeyPersonID            = "person_id"
	sessionKeyOrgID               = "org_id"
	sessionKeyWorkspaceID         = "workspace_id"
	sessionKeyOIDCSubject         = "oidc_subject"
	sessionKeyEmail               = "email"
	sessionKeyName                = "name"
	sessionKeyUsername            = "username"
	sessionKeyRoles               = "roles"
	// OIDC flow keys (temporary)
	sessionKeyState         = "state"
	sessionKeyNonce         = "nonce"
	sessionKeyCodeVerifier  = "code_verifier"
	sessionKeyStateIssuedAt = "state_issued_at"
	// sessionKeyReturnTo is the same-origin path the auth middleware
	// recorded before bouncing an unauthenticated request to /login
	// (ACC-9); CallbackHandler consumes and clears it via resolveReturnTo.
	sessionKeyReturnTo = "return_to"
)

// loginStateReuseWindow bounds how long a pending (unconsumed) OIDC flow is
// reused by subsequent /login hits instead of being regenerated. Long enough
// to cover parallel redirects from one navigation plus a user pausing at the
// IdP form; short enough that an abandoned flow's state has a bounded life.
const loginStateReuseWindow = 5 * time.Minute

// loginSessionDeadline is how long a session /login creates lives before a
// callback completes: the state freshness window above plus headroom for a
// person to get through a second factor at the identity provider (design
// D3). A successful callback replaces this with the full session lifetime.
const loginSessionDeadline = 15 * time.Minute

// UserSession contains the authenticated user's session data.
// This provides type-safe access to session values.
type UserSession struct {
	PersonID    string
	OrgID       string
	WorkspaceID string
	OIDCSubject string
	Email       string
	Name        string
	Username    string
	Roles       []string
}

// GetUserSession retrieves the authenticated user's session data.
// Returns nil if the user is not authenticated.
func (c *Config) GetUserSession(ctx context.Context) *UserSession {
	if !c.SessionManager.GetBool(ctx, sessionKeyAuthenticated) {
		return nil
	}

	return &UserSession{
		PersonID:    c.SessionManager.GetString(ctx, sessionKeyPersonID),
		OrgID:       c.SessionManager.GetString(ctx, sessionKeyOrgID),
		WorkspaceID: c.SessionManager.GetString(ctx, sessionKeyWorkspaceID),
		OIDCSubject: c.SessionManager.GetString(ctx, sessionKeyOIDCSubject),
		Email:       c.SessionManager.GetString(ctx, sessionKeyEmail),
		Name:        c.SessionManager.GetString(ctx, sessionKeyName),
		Username:    c.SessionManager.GetString(ctx, sessionKeyUsername),
		Roles:       c.getRoles(ctx),
	}
}

// GetPersonID returns the person UUID of the authenticated user.
// Returns empty string if the user is not authenticated.
func (c *Config) GetPersonID(ctx context.Context) string {
	return c.SessionManager.GetString(ctx, sessionKeyPersonID)
}

// GetOrgID returns the active organization UUID.
func (c *Config) GetOrgID(ctx context.Context) string {
	return c.SessionManager.GetString(ctx, sessionKeyOrgID)
}

// GetWorkspaceID returns the active workspace UUID.
func (c *Config) GetWorkspaceID(ctx context.Context) string {
	return c.SessionManager.GetString(ctx, sessionKeyWorkspaceID)
}

// GetUserEmail returns the email of the authenticated user.
func (c *Config) GetUserEmail(ctx context.Context) string {
	return c.SessionManager.GetString(ctx, sessionKeyEmail)
}

// GetUserName returns the display name of the authenticated user.
func (c *Config) GetUserName(ctx context.Context) string {
	return c.SessionManager.GetString(ctx, sessionKeyName)
}

// GetUsername returns the username of the authenticated user.
func (c *Config) GetUsername(ctx context.Context) string {
	return c.SessionManager.GetString(ctx, sessionKeyUsername)
}

// IsAuthenticated returns true if the user has an active session.
func (c *Config) IsAuthenticated(ctx context.Context) bool {
	return c.SessionManager.GetBool(ctx, sessionKeyAuthenticated)
}

// HasRole checks if the current user has the specified role.
func (c *Config) HasRole(r *http.Request, role string) bool {
	roles := c.getRoles(r.Context())
	for _, r := range roles {
		if r == role {
			return true
		}
	}
	return false
}

// getRoles retrieves the roles from session.
func (c *Config) getRoles(ctx context.Context) []string {
	roles, ok := c.SessionManager.Get(ctx, sessionKeyRoles).([]string)
	if !ok {
		return nil
	}
	return roles
}

// validReturnTo reports whether raw is safe to store, and later redirect
// to, as the page to return to after sign-in (ACC-9): a same-origin
// relative reference starting with a single "/" and carrying no scheme or
// host of its own. A leading "//" is rejected outright — a browser
// resolves it as protocol-relative to whatever host follows, the same
// open-redirect shape as an absolute URL — even though url.Parse would
// also catch it via a non-empty Host.
func validReturnTo(raw string) (string, bool) {
	if raw == "" || raw[0] != '/' || strings.HasPrefix(raw, "//") {
		return "", false
	}
	// Browsers parse a backslash in an http(s) URL as a slash (WHATWG URL,
	// "special scheme"), so "/\evil.example" is "//evil.example" to the
	// browser and a same-origin path to net/url. No console path contains
	// one; refuse them all rather than model the browser's parser (2026-09
	// audit candidate "Open redirect via backslash").
	if strings.Contains(raw, "\\") {
		return "", false
	}
	u, err := url.Parse(raw)
	if err != nil || u.IsAbs() || u.Host != "" {
		return "", false
	}
	return raw, true
}

// sameOriginReturnTo validates referer (an HTMX request's own Referer
// header — the document that issued the fetch, since the fetch's own URL
// is a partial endpoint, not a page to land on) as a same-origin URL
// matching the incoming request's Host, and returns its path plus query
// the way validReturnTo treats a direct GET request's own URL.
func sameOriginReturnTo(referer string, r *http.Request) (string, bool) {
	if referer == "" {
		return "", false
	}
	u, err := url.Parse(referer)
	if err != nil || !u.IsAbs() || u.Host != r.Host {
		return "", false
	}
	return validReturnTo(u.RequestURI())
}

// Helper function to generate random strings
func generateRandomString(n int) string {
	b := make([]byte, n)
	if _, err := rand.Read(b); err != nil {
		// Unreachable on a working system: crypto/rand.Read never
		// returns an error. If the entropy source is gone there is no
		// safe degraded behaviour — every caller here is minting a
		// CSRF-grade secret — so the process stops rather than issue a
		// guessable state, nonce or code verifier.
		panic(fmt.Sprintf("auth: no entropy for a random string: %v", err))
	}
	return base64.RawURLEncoding.EncodeToString(b)
}

// claimsReader is the part of *oidc.IDToken that rolesFromIDToken needs, so
// the role path can be exercised in tests without a signed token.
type claimsReader interface {
	Claims(v any) error
}

// roleClaimLocations are the claim keys extractRoles reads. Their presence
// (even empty) is what tells a correctly mapped ID token apart from one the
// IdP never mapped roles into.
var roleClaimLocations = []string{"roles", "groups", "realm_access", "resource_access"}

// rolesFromIDToken reads roles from the verified ID token. The ID token is
// the token OIDC defines for the client to consume, and by the time it
// reaches here it has passed signature and nonce verification. The access
// token is deliberately not read: OAuth2 leaves its format opaque, so parsing
// it as a JWT only works with IdPs that happen to issue JWT access tokens,
// and with any other IdP every operator would silently receive no roles.
//
// An ID token carrying none of the role claim locations at all is logged
// loudly: that shape means the IdP is not mapping roles into the ID token
// (docs/identity-provider-setup.md), and without the log the only symptom
// is an operator who cannot get in. A location that is present but empty is
// an ordinary member with no roles and is not logged.
func rolesFromIDToken(ctx context.Context, idToken claimsReader, clientID, email string) []string {
	logger := logging.FromContext(ctx)
	var present map[string]json.RawMessage
	if err := idToken.Claims(&present); err != nil {
		logger.Error("could not parse the ID token's claims while reading roles",
			slog.Any("error", err))
		return nil
	}
	if !hasRoleClaimLocation(present) {
		logger.Warn("ID token carries no role claims; the identity provider must map roles into the ID token, see docs/identity-provider-setup.md",
			slog.String("email", email),
			slog.String("expected_claims", strings.Join(roleClaimLocations, ", ")))
		return nil
	}
	var claims rolesClaims
	if err := idToken.Claims(&claims); err != nil {
		logger.Error("could not parse roles from the ID token",
			slog.Any("error", err))
		return nil
	}
	return extractRoles(claims, clientID)
}

// hasRoleClaimLocation reports whether any of roleClaimLocations is present
// in the decoded claims, regardless of its value.
func hasRoleClaimLocation(claims map[string]json.RawMessage) bool {
	for _, key := range roleClaimLocations {
		if _, ok := claims[key]; ok {
			return true
		}
	}
	return false
}

// rolesClaims is the subset of ID-token claims that may carry roles,
// across IdPs: top-level roles/groups (generic), realm_access (Keycloak
// realm roles), and resource_access (Keycloak client-scoped roles, keyed by
// client ID).
type rolesClaims struct {
	Roles       []string `json:"roles"`
	Groups      []string `json:"groups"`
	RealmAccess struct {
		Roles []string `json:"roles"`
	} `json:"realm_access"`
	ResourceAccess map[string]struct {
		Roles []string `json:"roles"`
	} `json:"resource_access"`
}

// extractRoles merges every claim location an IdP may put roles in, rather
// than letting the first non-empty location mask the rest: a deployment's
// role names are its contract, and they count wherever the IdP carries them.
// The result is deduplicated and order-stable (source order above, then
// claim order). clientID scopes the resource_access lookup to this app's
// OIDC client; other clients' roles never leak in.
func extractRoles(claims rolesClaims, clientID string) []string {
	var merged []string
	seen := make(map[string]struct{})
	add := func(roles []string) {
		for _, role := range roles {
			if _, dup := seen[role]; dup {
				continue
			}
			seen[role] = struct{}{}
			merged = append(merged, role)
		}
	}
	add(claims.Roles)
	add(claims.Groups)
	add(claims.RealmAccess.Roles)
	add(claims.ResourceAccess[clientID].Roles)
	return merged
}

// idTokenUsableAsHint reports whether the stored raw ID token is still
// worth sending as an OIDC id_token_hint. The exp claim is read without
// signature verification: this only decides whether to attach the hint,
// and the IdP re-verifies whatever it receives. A malformed token is not
// usable. The 30-second headroom covers the redirect hop.
func idTokenUsableAsHint(raw string, now time.Time) bool {
	parts := strings.Split(raw, ".")
	if len(parts) != 3 {
		return false
	}
	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return false
	}
	var claims struct {
		Exp int64 `json:"exp"`
	}
	if err := json.Unmarshal(payload, &claims); err != nil || claims.Exp == 0 {
		return false
	}
	return now.Add(30*time.Second).Unix() < claims.Exp
}