3 files changed, 244 insertions, 0 deletions
diff --git a/services/auth/auth_token.go b/services/auth/auth_token.go
new file mode 100644
index 0000000000..6b59238c98
--- /dev/null
+++ b/services/auth/auth_token.go
@@ -0,0 +1,123 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package auth
+
+import (
+	"context"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/hex"
+	"errors"
+	"strings"
+	"time"
+
+	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
+)
+
+// Based on https://paragonie.com/blog/2015/04/secure-authentication-php-with-long-term-persistence#secure-remember-me-cookies
+
+// The auth token consists of two parts: ID and token hash
+// Every device login creates a new auth token with an individual id and hash.
+// If a device uses the token to login into the instance, a fresh token gets generated which has the same id but a new hash.
+
+var (
+	ErrAuthTokenInvalidFormat = util.NewInvalidArgumentErrorf("auth token has an invalid format")
+	ErrAuthTokenExpired       = util.NewInvalidArgumentErrorf("auth token has expired")
+	ErrAuthTokenInvalidHash   = util.NewInvalidArgumentErrorf("auth token is invalid")
+)
+
+func CheckAuthToken(ctx context.Context, value string) (*auth_model.AuthToken, error) {
+	if len(value) == 0 {
+		return nil, nil
+	}
+
+	parts := strings.SplitN(value, ":", 2)
+	if len(parts) != 2 {
+		return nil, ErrAuthTokenInvalidFormat
+	}
+
+	t, err := auth_model.GetAuthTokenByID(ctx, parts[0])
+	if err != nil {
+		if errors.Is(err, util.ErrNotExist) {
+			return nil, ErrAuthTokenExpired
+		}
+		return nil, err
+	}
+
+	if t.ExpiresUnix < timeutil.TimeStampNow() {
+		return nil, ErrAuthTokenExpired
+	}
+
+	hashedToken := sha256.Sum256([]byte(parts[1]))
+
+	if subtle.ConstantTimeCompare([]byte(t.TokenHash), []byte(hex.EncodeToString(hashedToken[:]))) == 0 {
+		// If an attacker steals a token and uses the token to create a new session the hash gets updated.
+		// When the victim uses the old token the hashes don't match anymore and the victim should be notified about the compromised token.
+		return nil, ErrAuthTokenInvalidHash
+	}
+
+	return t, nil
+}
+
+func RegenerateAuthToken(ctx context.Context, t *auth_model.AuthToken) (*auth_model.AuthToken, string, error) {
+	token, hash, err := generateTokenAndHash()
+	if err != nil {
+		return nil, "", err
+	}
+
+	newToken := &auth_model.AuthToken{
+		ID:          t.ID,
+		TokenHash:   hash,
+		UserID:      t.UserID,
+		ExpiresUnix: timeutil.TimeStampNow().AddDuration(time.Duration(setting.LogInRememberDays*24) * time.Hour),
+	}
+
+	if err := auth_model.UpdateAuthTokenByID(ctx, newToken); err != nil {
+		return nil, "", err
+	}
+
+	return newToken, token, nil
+}
+
+func CreateAuthTokenForUserID(ctx context.Context, userID int64) (*auth_model.AuthToken, string, error) {
+	t := &auth_model.AuthToken{
+		UserID:      userID,
+		ExpiresUnix: timeutil.TimeStampNow().AddDuration(time.Duration(setting.LogInRememberDays*24) * time.Hour),
+	}
+
+	var err error
+	t.ID, err = util.CryptoRandomString(10)
+	if err != nil {
+		return nil, "", err
+	}
+
+	token, hash, err := generateTokenAndHash()
+	if err != nil {
+		return nil, "", err
+	}
+
+	t.TokenHash = hash
+
+	if err := auth_model.InsertAuthToken(ctx, t); err != nil {
+		return nil, "", err
+	}
+
+	return t, token, nil
+}
+
+func generateTokenAndHash() (string, string, error) {
+	buf, err := util.CryptoRandomBytes(32)
+	if err != nil {
+		return "", "", err
+	}
+
+	token := hex.EncodeToString(buf)
+
+	hashedToken := sha256.Sum256([]byte(token))
+
+	return token, hex.EncodeToString(hashedToken[:]), nil
+}
diff --git a/services/auth/auth_token_test.go b/services/auth/auth_token_test.go
new file mode 100644
index 0000000000..654275df17
--- /dev/null
+++ b/services/auth/auth_token_test.go
@@ -0,0 +1,107 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package auth
+
+import (
+	"testing"
+	"time"
+
+	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/timeutil"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCheckAuthToken(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	t.Run("Empty", func(t *testing.T) {
+		token, err := CheckAuthToken(db.DefaultContext, "")
+		assert.NoError(t, err)
+		assert.Nil(t, token)
+	})
+
+	t.Run("InvalidFormat", func(t *testing.T) {
+		token, err := CheckAuthToken(db.DefaultContext, "dummy")
+		assert.ErrorIs(t, err, ErrAuthTokenInvalidFormat)
+		assert.Nil(t, token)
+	})
+
+	t.Run("NotFound", func(t *testing.T) {
+		token, err := CheckAuthToken(db.DefaultContext, "notexists:dummy")
+		assert.ErrorIs(t, err, ErrAuthTokenExpired)
+		assert.Nil(t, token)
+	})
+
+	t.Run("Expired", func(t *testing.T) {
+		timeutil.Set(time.Date(2023, 1, 1, 0, 0, 0, 0, time.UTC))
+
+		at, token, err := CreateAuthTokenForUserID(db.DefaultContext, 2)
+		assert.NoError(t, err)
+		assert.NotNil(t, at)
+		assert.NotEmpty(t, token)
+
+		timeutil.Unset()
+
+		at2, err := CheckAuthToken(db.DefaultContext, at.ID+":"+token)
+		assert.ErrorIs(t, err, ErrAuthTokenExpired)
+		assert.Nil(t, at2)
+
+		assert.NoError(t, auth_model.DeleteAuthTokenByID(db.DefaultContext, at.ID))
+	})
+
+	t.Run("InvalidHash", func(t *testing.T) {
+		at, token, err := CreateAuthTokenForUserID(db.DefaultContext, 2)
+		assert.NoError(t, err)
+		assert.NotNil(t, at)
+		assert.NotEmpty(t, token)
+
+		at2, err := CheckAuthToken(db.DefaultContext, at.ID+":"+token+"dummy")
+		assert.ErrorIs(t, err, ErrAuthTokenInvalidHash)
+		assert.Nil(t, at2)
+
+		assert.NoError(t, auth_model.DeleteAuthTokenByID(db.DefaultContext, at.ID))
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		at, token, err := CreateAuthTokenForUserID(db.DefaultContext, 2)
+		assert.NoError(t, err)
+		assert.NotNil(t, at)
+		assert.NotEmpty(t, token)
+
+		at2, err := CheckAuthToken(db.DefaultContext, at.ID+":"+token)
+		assert.NoError(t, err)
+		assert.NotNil(t, at2)
+
+		assert.NoError(t, auth_model.DeleteAuthTokenByID(db.DefaultContext, at.ID))
+	})
+}
+
+func TestRegenerateAuthToken(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	timeutil.Set(time.Date(2023, 1, 1, 0, 0, 0, 0, time.UTC))
+	defer timeutil.Unset()
+
+	at, token, err := CreateAuthTokenForUserID(db.DefaultContext, 2)
+	assert.NoError(t, err)
+	assert.NotNil(t, at)
+	assert.NotEmpty(t, token)
+
+	timeutil.Set(time.Date(2023, 1, 1, 0, 0, 1, 0, time.UTC))
+
+	at2, token2, err := RegenerateAuthToken(db.DefaultContext, at)
+	assert.NoError(t, err)
+	assert.NotNil(t, at2)
+	assert.NotEmpty(t, token2)
+
+	assert.Equal(t, at.ID, at2.ID)
+	assert.Equal(t, at.UserID, at2.UserID)
+	assert.NotEqual(t, token, token2)
+	assert.NotEqual(t, at.ExpiresUnix, at2.ExpiresUnix)
+
+	assert.NoError(t, auth_model.DeleteAuthTokenByID(db.DefaultContext, at.ID))
+}
diff --git a/services/auth/main_test.go b/services/auth/main_test.go
new file mode 100644
index 0000000000..b81c39a1f2
--- /dev/null
+++ b/services/auth/main_test.go
@@ -0,0 +1,14 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package auth
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/unittest"
+)
+
+func TestMain(m *testing.M) {
+	unittest.MainTest(m)
+}