[GITEA] rework long-term authentication

- The current architecture is inherently insecure, because you can
construct the 'secret' cookie value with values that are available in
the database. Thus provides zero protection when a database is
dumped/leaked.
- This patch implements a new architecture that's inspired from: [Paragonie Initiative](https://paragonie.com/blog/2015/04/secure-authentication-php-with-long-term-persistence#secure-remember-me-cookies).
- Integration testing is added to ensure the new mechanism works.
- Removes a setting, because it's not used anymore.

(cherry picked from commit eff097448b)

[GITEA] rework long-term authentication (squash) add migration

Reminder: the migration is run via integration tests as explained
in the commit "[DB] run all Forgejo migrations in integration tests"

(cherry picked from commit 4accf7443c)
(cherry picked from commit 99d06e344ebc3b50bafb2ac4473dd95f057d1ddc)
(cherry picked from commit d8bc98a8f0)
(cherry picked from commit 6404845df9)
(cherry picked from commit 72bdd4f3b9)
(cherry picked from commit 4b01bb0ce8)

tests/integration/auth_token_test.go

@@ -0,0 +1,163 @@
+// Copyright 2023 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"encoding/hex"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+
+	"code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/tests"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// GetSessionForLTACookie returns a new session with only the LTA cookie being set.
+func GetSessionForLTACookie(t *testing.T, ltaCookie *http.Cookie) *TestSession {
+	t.Helper()
+
+	ch := http.Header{}
+	ch.Add("Cookie", ltaCookie.String())
+	cr := http.Request{Header: ch}
+
+	session := emptyTestSession(t)
+	baseURL, err := url.Parse(setting.AppURL)
+	assert.NoError(t, err)
+	session.jar.SetCookies(baseURL, cr.Cookies())
+
+	return session
+}
+
+// GetLTACookieValue returns the value of the LTA cookie.
+func GetLTACookieValue(t *testing.T, sess *TestSession) string {
+	t.Helper()
+
+	rememberCookie := sess.GetCookie(setting.CookieRememberName)
+	assert.NotNil(t, rememberCookie)
+
+	cookieValue, err := url.QueryUnescape(rememberCookie.Value)
+	assert.NoError(t, err)
+
+	return cookieValue
+}
+
+// TestSessionCookie checks if the session cookie provides authentication.
+func TestSessionCookie(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	sess := loginUser(t, "user1")
+	assert.NotNil(t, sess.GetCookie(setting.SessionConfig.CookieName))
+
+	req := NewRequest(t, "GET", "/user/settings")
+	sess.MakeRequest(t, req, http.StatusOK)
+}
+
+// TestLTACookie checks if the LTA cookie that's returned is valid, exists in the database
+// and provides authentication of no session cookie is present.
+func TestLTACookie(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
+	sess := emptyTestSession(t)
+
+	req := NewRequestWithValues(t, "POST", "/user/login", map[string]string{
+		"_csrf":     GetCSRF(t, sess, "/user/login"),
+		"user_name": user.Name,
+		"password":  userPassword,
+		"remember":  "true",
+	})
+	sess.MakeRequest(t, req, http.StatusSeeOther)
+
+	// Checks if the database entry exist for the user.
+	ltaCookieValue := GetLTACookieValue(t, sess)
+	lookupKey, validator, found := strings.Cut(ltaCookieValue, ":")
+	assert.True(t, found)
+	rawValidator, err := hex.DecodeString(validator)
+	assert.NoError(t, err)
+	unittest.AssertExistsAndLoadBean(t, &auth.AuthorizationToken{LookupKey: lookupKey, HashedValidator: auth.HashValidator(rawValidator), UID: user.ID})
+
+	// Check if the LTA cookie it provides authentication.
+	// If LTA cookie provides authentication /user/login shouldn't return status 200.
+	session := GetSessionForLTACookie(t, sess.GetCookie(setting.CookieRememberName))
+	req = NewRequest(t, "GET", "/user/login")
+	session.MakeRequest(t, req, http.StatusSeeOther)
+}
+
+// TestLTAPasswordChange checks that LTA doesn't provide authentication when a
+// password change has happened and that the new LTA does provide authentication.
+func TestLTAPasswordChange(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
+
+	sess := loginUserWithPasswordRemember(t, user.Name, userPassword, true)
+	oldRememberCookie := sess.GetCookie(setting.CookieRememberName)
+	assert.NotNil(t, oldRememberCookie)
+
+	// Make a simple password change.
+	req := NewRequestWithValues(t, "POST", "/user/settings/account", map[string]string{
+		"_csrf":        GetCSRF(t, sess, "/user/settings/account"),
+		"old_password": userPassword,
+		"password":     "password2",
+		"retype":       "password2",
+	})
+	sess.MakeRequest(t, req, http.StatusSeeOther)
+	rememberCookie := sess.GetCookie(setting.CookieRememberName)
+	assert.NotNil(t, rememberCookie)
+
+	// Check if the password really changed.
+	assert.NotEqualValues(t, unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1}).Passwd, user.Passwd)
+
+	// /user/settings/account should provide with a new LTA cookie, so check for that.
+	// If LTA cookie provides authentication /user/login shouldn't return status 200.
+	session := GetSessionForLTACookie(t, rememberCookie)
+	req = NewRequest(t, "GET", "/user/login")
+	session.MakeRequest(t, req, http.StatusSeeOther)
+
+	// Check if the old LTA token is invalidated.
+	session = GetSessionForLTACookie(t, oldRememberCookie)
+	req = NewRequest(t, "GET", "/user/login")
+	session.MakeRequest(t, req, http.StatusOK)
+}
+
+// TestLTAExpiry tests that the LTA expiry works.
+func TestLTAExpiry(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
+
+	sess := loginUserWithPasswordRemember(t, user.Name, userPassword, true)
+
+	ltaCookieValie := GetLTACookieValue(t, sess)
+	lookupKey, _, found := strings.Cut(ltaCookieValie, ":")
+	assert.True(t, found)
+
+	// Ensure it's not expired.
+	lta := unittest.AssertExistsAndLoadBean(t, &auth.AuthorizationToken{UID: user.ID, LookupKey: lookupKey})
+	assert.False(t, lta.IsExpired())
+
+	// Manually stub LTA's expiry.
+	_, err := db.GetEngine(db.DefaultContext).ID(lta.ID).Table("forgejo_auth_token").Cols("expiry").Update(&auth.AuthorizationToken{Expiry: timeutil.TimeStampNow()})
+	assert.NoError(t, err)
+
+	// Ensure it's expired.
+	lta = unittest.AssertExistsAndLoadBean(t, &auth.AuthorizationToken{UID: user.ID, LookupKey: lookupKey})
+	assert.True(t, lta.IsExpired())
+
+	// Should return 200 OK, because LTA doesn't provide authorization anymore.
+	session := GetSessionForLTACookie(t, sess.GetCookie(setting.CookieRememberName))
+	req := NewRequest(t, "GET", "/user/login")
+	session.MakeRequest(t, req, http.StatusOK)
+
+	// Ensure it's deleted.
+	unittest.AssertNotExistsBean(t, &auth.AuthorizationToken{UID: user.ID, LookupKey: lookupKey})
+}