fix: extend forgejo_auth_token table

- Add a `purpose` column, this allows the `forgejo_auth_token` table to
be used by other parts of Forgejo, while still enjoying the
no-compromise architecture.
- Remove the 'roll your own crypto' time limited code functions and
migrate them to the `forgejo_auth_token` table. This migration ensures
generated codes can only be used for their purpose and ensure they are
invalidated after their usage by deleting it from the database, this
also should help making auditing of the security code easier, as we're
no longer trying to stuff a lot of data into a HMAC construction.
-Helper functions are rewritten to ensure a safe-by-design approach to
these tokens.
- Add the `forgejo_auth_token` to dbconsistency doctor and add it to the
`deleteUser` function.
- TODO: Add cron job to delete expired authorization tokens.
- Unit and integration tests added.

models/auth/auth_token.go

@@ -15,12 +15,31 @@ import (
 	"code.gitea.io/gitea/modules/util"
 )
 
+type AuthorizationPurpose string
+
+var (
+	// Used to store long term authorization tokens.
+	LongTermAuthorization AuthorizationPurpose = "long_term_authorization"
+
+	// Used to activate a user account.
+	UserActivation AuthorizationPurpose = "user_activation"
+
+	// Used to reset the password.
+	PasswordReset AuthorizationPurpose = "password_reset"
+)
+
+// Used to activate the specified email address for a user.
+func EmailActivation(email string) AuthorizationPurpose {
+	return AuthorizationPurpose("email_activation:" + email)
+}
+
 // AuthorizationToken represents a authorization token to a user.
 type AuthorizationToken struct {
 	ID              int64  `xorm:"pk autoincr"`
 	UID             int64  `xorm:"INDEX"`
 	LookupKey       string `xorm:"INDEX UNIQUE"`
 	HashedValidator string
+	Purpose         AuthorizationPurpose `xorm:"NOT NULL"`
 	Expiry          timeutil.TimeStamp
 }
 
@@ -41,7 +60,7 @@ func (authToken *AuthorizationToken) IsExpired() bool {
 // GenerateAuthToken generates a new authentication token for the given user.
 // It returns the lookup key and validator values that should be passed to the
 // user via a long-term cookie.
-func GenerateAuthToken(ctx context.Context, userID int64, expiry timeutil.TimeStamp) (lookupKey, validator string, err error) {
+func GenerateAuthToken(ctx context.Context, userID int64, expiry timeutil.TimeStamp, purpose AuthorizationPurpose) (lookupKey, validator string, err error) {
 	// Request 64 random bytes. The first 32 bytes will be used for the lookupKey
 	// and the other 32 bytes will be used for the validator.
 	rBytes, err := util.CryptoRandomBytes(64)
@@ -56,14 +75,15 @@ func GenerateAuthToken(ctx context.Context, userID int64, expiry timeutil.TimeSt
 		Expiry:          expiry,
 		LookupKey:       lookupKey,
 		HashedValidator: HashValidator(rBytes[32:]),
+		Purpose:         purpose,
 	})
 	return lookupKey, validator, err
 }
 
 // FindAuthToken will find a authorization token via the lookup key.
-func FindAuthToken(ctx context.Context, lookupKey string) (*AuthorizationToken, error) {
+func FindAuthToken(ctx context.Context, lookupKey string, purpose AuthorizationPurpose) (*AuthorizationToken, error) {
 	var authToken AuthorizationToken
-	has, err := db.GetEngine(ctx).Where("lookup_key = ?", lookupKey).Get(&authToken)
+	has, err := db.GetEngine(ctx).Where("lookup_key = ? AND purpose = ?", lookupKey, purpose).Get(&authToken)
 	if err != nil {
 		return nil, err
 	} else if !has {

models/forgejo_migrations/migrate.go

@@ -84,6 +84,8 @@ var migrations = []*Migration{
 	NewMigration("Add `legacy` to `web_authn_credential` table", AddLegacyToWebAuthnCredential),
 	// v23 -> v24
 	NewMigration("Add `delete_branch_after_merge` to `auto_merge` table", AddDeleteBranchAfterMergeToAutoMerge),
+	// v24 -> v25
+	NewMigration("Add `purpose` column to `forgejo_auth_token` table", AddPurposeToForgejoAuthToken),
 }
 
 // GetCurrentDBVersion returns the current Forgejo database version.

models/forgejo_migrations/v24.go

@@ -0,0 +1,19 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package forgejo_migrations //nolint:revive
+
+import "xorm.io/xorm"
+
+func AddPurposeToForgejoAuthToken(x *xorm.Engine) error {
+	type ForgejoAuthToken struct {
+		ID      int64  `xorm:"pk autoincr"`
+		Purpose string `xorm:"NOT NULL"`
+	}
+	if err := x.Sync(new(ForgejoAuthToken)); err != nil {
+		return err
+	}
+
+	_, err := x.Exec("UPDATE `forgejo_auth_token` SET purpose = 'long_term_authorization' WHERE purpose = ''")
+	return err
+}

models/user/email_address.go

@@ -8,10 +8,8 @@ import (
 	"context"
 	"fmt"
 	"strings"
-	"time"
 
 	"code.gitea.io/gitea/models/db"
-	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/setting"
@@ -246,23 +244,6 @@ func updateActivation(ctx context.Context, email *EmailAddress, activate bool) e
 	return UpdateUserCols(ctx, user, "rands")
 }
 
-// VerifyActiveEmailCode verifies active email code when active account
-func VerifyActiveEmailCode(ctx context.Context, code, email string) *EmailAddress {
-	if user := GetVerifyUser(ctx, code); user != nil {
-		// time limit code
-		prefix := code[:base.TimeLimitCodeLength]
-		data := fmt.Sprintf("%d%s%s%s%s", user.ID, email, user.LowerName, user.Passwd, user.Rands)
-
-		if base.VerifyTimeLimitCode(time.Now(), data, setting.Service.ActiveCodeLives, prefix) {
-			emailAddress := &EmailAddress{UID: user.ID, Email: email}
-			if has, _ := db.GetEngine(ctx).Get(emailAddress); has {
-				return emailAddress
-			}
-		}
-	}
-	return nil
-}
-
 // SearchEmailOrderBy is used to sort the results from SearchEmails()
 type SearchEmailOrderBy string
 

models/user/user.go

@@ -7,7 +7,9 @@ package user
 
 import (
 	"context"
+	"crypto/subtle"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"net/mail"
 	"net/url"
@@ -318,15 +320,14 @@ func (u *User) OrganisationLink() string {
 	return setting.AppSubURL + "/org/" + url.PathEscape(u.Name)
 }
 
-// GenerateEmailActivateCode generates an activate code based on user information and given e-mail.
-func (u *User) GenerateEmailActivateCode(email string) string {
-	code := base.CreateTimeLimitCode(
-		fmt.Sprintf("%d%s%s%s%s", u.ID, email, u.LowerName, u.Passwd, u.Rands),
-		setting.Service.ActiveCodeLives, time.Now(), nil)
-
-	// Add tail hex username
-	code += hex.EncodeToString([]byte(u.LowerName))
-	return code
+// GenerateEmailAuthorizationCode generates an activation code based for the user for the specified purpose.
+// The standard expiry is ActiveCodeLives minutes.
+func (u *User) GenerateEmailAuthorizationCode(ctx context.Context, purpose auth.AuthorizationPurpose) (string, error) {
+	lookup, validator, err := auth.GenerateAuthToken(ctx, u.ID, timeutil.TimeStampNow().Add(int64(setting.Service.ActiveCodeLives)*60), purpose)
+	if err != nil {
+		return "", err
+	}
+	return lookup + ":" + validator, nil
 }
 
 // GetUserFollowers returns range of user's followers.
@@ -838,35 +839,50 @@ func countUsers(ctx context.Context, opts *CountUserFilter) int64 {
 	return count
 }
 
-// GetVerifyUser get user by verify code
-func GetVerifyUser(ctx context.Context, code string) (user *User) {
-	if len(code) <= base.TimeLimitCodeLength {
-		return nil
+// VerifyUserActiveCode verifies that the code is valid for the given purpose for this user.
+// If delete is specified, the token will be deleted.
+func VerifyUserAuthorizationToken(ctx context.Context, code string, purpose auth.AuthorizationPurpose, delete bool) (*User, error) {
+	lookupKey, validator, found := strings.Cut(code, ":")
+	if !found {
+		return nil, nil
 	}
 
-	// use tail hex username query user
-	hexStr := code[base.TimeLimitCodeLength:]
-	if b, err := hex.DecodeString(hexStr); err == nil {
-		if user, err = GetUserByName(ctx, string(b)); user != nil {
-			return user
+	authToken, err := auth.FindAuthToken(ctx, lookupKey, purpose)
+	if err != nil {
+		if errors.Is(err, util.ErrNotExist) {
+			return nil, nil
 		}
-		log.Error("user.getVerifyUser: %v", err)
+		return nil, err
 	}
 
-	return nil
-}
+	if authToken.IsExpired() {
+		return nil, auth.DeleteAuthToken(ctx, authToken)
+	}
 
-// VerifyUserActiveCode verifies active code when active account
-func VerifyUserActiveCode(ctx context.Context, code string) (user *User) {
-	if user = GetVerifyUser(ctx, code); user != nil {
-		// time limit code
-		prefix := code[:base.TimeLimitCodeLength]
-		data := fmt.Sprintf("%d%s%s%s%s", user.ID, user.Email, user.LowerName, user.Passwd, user.Rands)
-		if base.VerifyTimeLimitCode(time.Now(), data, setting.Service.ActiveCodeLives, prefix) {
-			return user
+	rawValidator, err := hex.DecodeString(validator)
+	if err != nil {
+		return nil, err
+	}
+
+	if subtle.ConstantTimeCompare([]byte(authToken.HashedValidator), []byte(auth.HashValidator(rawValidator))) == 0 {
+		return nil, errors.New("validator doesn't match")
+	}
+
+	u, err := GetUserByID(ctx, authToken.UID)
+	if err != nil {
+		if IsErrUserNotExist(err) {
+			return nil, nil
+		}
+		return nil, err
+	}
+
+	if delete {
+		if err := auth.DeleteAuthToken(ctx, authToken); err != nil {
+			return nil, err
 		}
 	}
-	return nil
+
+	return u, nil
 }
 
 // ValidateUser check if user is valid to insert / update into database

models/user/user_test.go

@@ -7,6 +7,7 @@ package user_test
 import (
 	"context"
 	"crypto/rand"
+	"encoding/hex"
 	"fmt"
 	"strings"
 	"testing"
@@ -21,7 +22,9 @@ import (
 	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/test"
 	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/validation"
 	"code.gitea.io/gitea/tests"
 
@@ -700,3 +703,66 @@ func TestDisabledUserFeatures(t *testing.T) {
 		assert.True(t, user_model.IsFeatureDisabledWithLoginType(user, f))
 	}
 }
+
+func TestGenerateEmailAuthorizationCode(t *testing.T) {
+	defer test.MockVariableValue(&setting.Service.ActiveCodeLives, 2)()
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+
+	code, err := user.GenerateEmailAuthorizationCode(db.DefaultContext, auth.UserActivation)
+	require.NoError(t, err)
+
+	lookupKey, validator, ok := strings.Cut(code, ":")
+	assert.True(t, ok)
+
+	rawValidator, err := hex.DecodeString(validator)
+	require.NoError(t, err)
+
+	authToken, err := auth.FindAuthToken(db.DefaultContext, lookupKey, auth.UserActivation)
+	require.NoError(t, err)
+	assert.False(t, authToken.IsExpired())
+	assert.EqualValues(t, authToken.HashedValidator, auth.HashValidator(rawValidator))
+
+	authToken.Expiry = authToken.Expiry.Add(-int64(setting.Service.ActiveCodeLives) * 60)
+	assert.True(t, authToken.IsExpired())
+}
+
+func TestVerifyUserAuthorizationToken(t *testing.T) {
+	defer test.MockVariableValue(&setting.Service.ActiveCodeLives, 2)()
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+
+	code, err := user.GenerateEmailAuthorizationCode(db.DefaultContext, auth.UserActivation)
+	require.NoError(t, err)
+
+	lookupKey, _, ok := strings.Cut(code, ":")
+	assert.True(t, ok)
+
+	t.Run("Wrong purpose", func(t *testing.T) {
+		u, err := user_model.VerifyUserAuthorizationToken(db.DefaultContext, code, auth.PasswordReset, false)
+		require.NoError(t, err)
+		assert.Nil(t, u)
+	})
+
+	t.Run("No delete", func(t *testing.T) {
+		u, err := user_model.VerifyUserAuthorizationToken(db.DefaultContext, code, auth.UserActivation, false)
+		require.NoError(t, err)
+		assert.EqualValues(t, user.ID, u.ID)
+
+		authToken, err := auth.FindAuthToken(db.DefaultContext, lookupKey, auth.UserActivation)
+		require.NoError(t, err)
+		assert.NotNil(t, authToken)
+	})
+
+	t.Run("Delete", func(t *testing.T) {
+		u, err := user_model.VerifyUserAuthorizationToken(db.DefaultContext, code, auth.UserActivation, true)
+		require.NoError(t, err)
+		assert.EqualValues(t, user.ID, u.ID)
+
+		authToken, err := auth.FindAuthToken(db.DefaultContext, lookupKey, auth.UserActivation)
+		require.ErrorIs(t, err, util.ErrNotExist)
+		assert.Nil(t, authToken)
+	})
+}