diff --git a/models/auth/source.go b/models/auth/source.go
index 8dd1cd4759..537cdde70b 100644
--- a/models/auth/source.go
+++ b/models/auth/source.go
@@ -33,6 +33,9 @@ const (
 	SSPI        // 7
 )
 
+// This should be in the above list of types but is separated to avoid conflicts with Gitea changes
+const F3 Type = 129
+
 // String returns the string name of the LoginType
 func (typ Type) String() string {
 	return Names[typ]
@@ -51,6 +54,7 @@ var Names = map[Type]string{
 	PAM:    "PAM",
 	OAuth2: "OAuth2",
 	SSPI:   "SPNEGO with SSPI",
+	F3:     "F3",
 }
 
 // Config represents login config as far as the db is concerned
@@ -179,6 +183,10 @@ func (source *Source) IsSSPI() bool {
 	return source.Type == SSPI
 }
 
+func (source *Source) IsF3() bool {
+	return source.Type == F3
+}
+
 // HasTLS returns true of this source supports TLS.
 func (source *Source) HasTLS() bool {
 	hasTLSer, ok := source.Cfg.(HasTLSer)
diff --git a/routers/web/auth/oauth.go b/routers/web/auth/oauth.go
index db15bf2e3d..6a771778d3 100644
--- a/routers/web/auth/oauth.go
+++ b/routers/web/auth/oauth.go
@@ -33,6 +33,7 @@ import (
 	source_service "code.gitea.io/gitea/services/auth/source"
 	"code.gitea.io/gitea/services/auth/source/oauth2"
 	"code.gitea.io/gitea/services/externalaccount"
+	f3_service "code.gitea.io/gitea/services/f3"
 	"code.gitea.io/gitea/services/forms"
 	user_service "code.gitea.io/gitea/services/user"
 
@@ -1208,9 +1209,21 @@ func handleOAuth2SignIn(ctx *context.Context, source *auth.Source, u *user_model
 	ctx.Redirect(setting.AppSubURL + "/user/two_factor")
 }
 
-// OAuth2UserLoginCallback attempts to handle the callback from the OAuth2 provider and if successful
-// login the user
 func oAuth2UserLoginCallback(authSource *auth.Source, request *http.Request, response http.ResponseWriter) (*user_model.User, goth.User, error) {
+	gothUser, err := oAuth2FetchUser(authSource, request, response)
+	if err != nil {
+		return nil, goth.User{}, err
+	}
+
+	if err := f3_service.MaybePromoteF3User(request.Context(), authSource, gothUser.UserID, gothUser.Email); err != nil {
+		return nil, goth.User{}, err
+	}
+
+	u, err := oAuth2GothUserToUser(request.Context(), authSource, gothUser)
+	return u, gothUser, err
+}
+
+func oAuth2FetchUser(authSource *auth.Source, request *http.Request, response http.ResponseWriter) (goth.User, error) {
 	oauth2Source := authSource.Cfg.(*oauth2.Source)
 
 	// Make sure that the response is not an error response.
@@ -1222,10 +1235,10 @@ func oAuth2UserLoginCallback(authSource *auth.Source, request *http.Request, res
 		// Delete the goth session
 		err := gothic.Logout(response, request)
 		if err != nil {
-			return nil, goth.User{}, err
+			return goth.User{}, err
 		}
 
-		return nil, goth.User{}, errCallback{
+		return goth.User{}, errCallback{
 			Code:        errorName,
 			Description: errorDescription,
 		}
@@ -1238,24 +1251,28 @@ func oAuth2UserLoginCallback(authSource *auth.Source, request *http.Request, res
 			log.Error("OAuth2 Provider %s returned too long a token. Current max: %d. Either increase the [OAuth2] MAX_TOKEN_LENGTH or reduce the information returned from the OAuth2 provider", authSource.Name, setting.OAuth2.MaxTokenLength)
 			err = fmt.Errorf("OAuth2 Provider %s returned too long a token. Current max: %d. Either increase the [OAuth2] MAX_TOKEN_LENGTH or reduce the information returned from the OAuth2 provider", authSource.Name, setting.OAuth2.MaxTokenLength)
 		}
-		return nil, goth.User{}, err
+		return goth.User{}, err
 	}
 
 	if oauth2Source.RequiredClaimName != "" {
 		claimInterface, has := gothUser.RawData[oauth2Source.RequiredClaimName]
 		if !has {
-			return nil, goth.User{}, user_model.ErrUserProhibitLogin{Name: gothUser.UserID}
+			return goth.User{}, user_model.ErrUserProhibitLogin{Name: gothUser.UserID}
 		}
 
 		if oauth2Source.RequiredClaimValue != "" {
 			groups := claimValueToStringSet(claimInterface)
 
 			if !groups.Contains(oauth2Source.RequiredClaimValue) {
-				return nil, goth.User{}, user_model.ErrUserProhibitLogin{Name: gothUser.UserID}
+				return goth.User{}, user_model.ErrUserProhibitLogin{Name: gothUser.UserID}
 			}
 		}
 	}
 
+	return gothUser, nil
+}
+
+func oAuth2GothUserToUser(ctx go_context.Context, authSource *auth.Source, gothUser goth.User) (*user_model.User, error) {
 	user := &user_model.User{
 		LoginName:   gothUser.UserID,
 		LoginType:   auth.OAuth2,
@@ -1264,12 +1281,13 @@ func oAuth2UserLoginCallback(authSource *auth.Source, request *http.Request, res
 
 	hasUser, err := user_model.GetUser(user)
 	if err != nil {
-		return nil, goth.User{}, err
+		return nil, err
 	}
 
 	if hasUser {
-		return user, gothUser, nil
+		return user, nil
 	}
+	log.Debug("no user found for LoginName %v, LoginSource %v, LoginType %v", user.LoginName, user.LoginSource, user.LoginType)
 
 	// search in external linked users
 	externalLoginUser := &user_model.ExternalLoginUser{
@@ -1278,13 +1296,13 @@ func oAuth2UserLoginCallback(authSource *auth.Source, request *http.Request, res
 	}
 	hasUser, err = user_model.GetExternalLogin(externalLoginUser)
 	if err != nil {
-		return nil, goth.User{}, err
+		return nil, err
 	}
 	if hasUser {
-		user, err = user_model.GetUserByID(request.Context(), externalLoginUser.UserID)
-		return user, gothUser, err
+		user, err = user_model.GetUserByID(ctx, externalLoginUser.UserID)
+		return user, err
 	}
 
 	// no user found to login
-	return nil, gothUser, nil
+	return nil, nil
 }
diff --git a/services/auth/source/f3/source.go b/services/auth/source/f3/source.go
new file mode 100644
index 0000000000..800e4baea3
--- /dev/null
+++ b/services/auth/source/f3/source.go
@@ -0,0 +1,33 @@
+// SPDX-FileCopyrightText: Copyright the Forgejo contributors
+// SPDX-License-Identifier: MIT
+
+package f3
+
+import (
+	"code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/modules/json"
+)
+
+type Source struct {
+	URL            string
+	MatchingSource string
+
+	// reference to the authSource
+	authSource *auth.Source
+}
+
+func (source *Source) FromDB(bs []byte) error {
+	return json.UnmarshalHandleDoubleEncode(bs, &source)
+}
+
+func (source *Source) ToDB() ([]byte, error) {
+	return json.Marshal(source)
+}
+
+func (source *Source) SetAuthSource(authSource *auth.Source) {
+	source.authSource = authSource
+}
+
+func init() {
+	auth.RegisterTypeConfig(auth.F3, &Source{})
+}
diff --git a/services/f3/promote.go b/services/f3/promote.go
new file mode 100644
index 0000000000..b11ff83a19
--- /dev/null
+++ b/services/f3/promote.go
@@ -0,0 +1,110 @@
+// SPDX-FileCopyrightText: Copyright the Forgejo contributors
+// SPDX-License-Identifier: MIT
+
+package f3
+
+import (
+	"context"
+
+	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/log"
+	f3_source "code.gitea.io/gitea/services/auth/source/f3"
+	"code.gitea.io/gitea/services/auth/source/oauth2"
+)
+
+func getUserByLoginName(ctx context.Context, name string) (*user_model.User, error) {
+	if len(name) == 0 {
+		return nil, user_model.ErrUserNotExist{Name: name}
+	}
+	u := &user_model.User{LoginName: name, LoginType: auth_model.F3, Type: user_model.UserTypeRemoteUser}
+	has, err := db.GetEngine(ctx).Get(u)
+	if err != nil {
+		return nil, err
+	} else if !has {
+		return nil, user_model.ErrUserNotExist{Name: name}
+	}
+	return u, nil
+}
+
+// The user created by F3 has:
+//
+//	Type        UserTypeRemoteUser
+//	LogingType  F3
+//	LoginName   set to the unique identifier of the originating forge
+//	LoginSource set to the F3 source that can be matched against a OAuth2 source
+//
+// If the source from which an authentification happens is OAuth2, a existing
+// F3 user will be promoted to an OAuth2 user provided:
+//
+//	user.LoginName is the same as goth.UserID (argument loginName)
+//	user.LoginSource has a MatchingSource equals to the name of the OAuth2 provider
+//
+// Once promoted, the user will be logged in without further interaction from the
+// user and will own all repositories, issues, etc. associated with it.
+func MaybePromoteF3User(ctx context.Context, source *auth_model.Source, loginName, email string) error {
+	user, err := getF3UserToPromote(ctx, source, loginName, email)
+	if err != nil {
+		return err
+	}
+	if user != nil {
+		promote := &user_model.User{
+			ID:          user.ID,
+			Type:        user_model.UserTypeIndividual,
+			Email:       email,
+			LoginSource: source.ID,
+			LoginType:   source.Type,
+		}
+		log.Debug("promote user %v: LoginName %v => %v, LoginSource %v => %v, LoginType %v => %v, Email %v => %v", user.ID, user.LoginName, promote.LoginName, user.LoginSource, promote.LoginSource, user.LoginType, promote.LoginType, user.Email, promote.Email)
+		return user_model.UpdateUser(ctx, promote, true, "type", "email", "login_source", "login_type")
+	}
+	return nil
+}
+
+func getF3UserToPromote(ctx context.Context, source *auth_model.Source, loginName, email string) (*user_model.User, error) {
+	if !source.IsOAuth2() {
+		log.Debug("getF3UserToPromote: source %v is not OAuth2", source)
+		return nil, nil
+	}
+	oauth2Source, ok := source.Cfg.(*oauth2.Source)
+	if !ok {
+		log.Error("getF3UserToPromote: source claims to be OAuth2 but really is %v", oauth2Source)
+		return nil, nil
+	}
+
+	u, err := getUserByLoginName(ctx, loginName)
+	if err != nil {
+		if user_model.IsErrUserNotExist(err) {
+			log.Debug("getF3UserToPromote: no user with LoginType F3 and LoginName '%s'", loginName)
+			return nil, nil
+		}
+		return nil, err
+	}
+
+	if u.Email != "" {
+		log.Debug("getF3UserToPromote: the user email is already set to '%s'", u.Email)
+		return nil, nil
+	}
+
+	userSource, err := auth_model.GetSourceByID(u.LoginSource)
+	if err != nil {
+		if auth_model.IsErrSourceNotExist(err) {
+			log.Error("getF3UserToPromote: source id = %v for user %v not found %v", u.LoginSource, u.ID, err)
+			return nil, nil
+		}
+		return nil, err
+	}
+	f3Source, ok := userSource.Cfg.(*f3_source.Source)
+	if !ok {
+		log.Error("getF3UserToPromote: expected an F3 source but got %T %v", userSource, userSource)
+		return nil, nil
+	}
+
+	if oauth2Source.Provider != f3Source.MatchingSource {
+		log.Debug("getF3UserToPromote: skip OAuth2 source %s because it is different from %s which is the expected match for the F3 source %s", oauth2Source.Provider, f3Source.MatchingSource, f3Source.URL)
+		return nil, nil
+	}
+
+	return u, nil
+}
diff --git a/tests/integration/f3_test.go b/tests/integration/f3_test.go
index 6c3ba75c07..3c213fef5c 100644
--- a/tests/integration/f3_test.go
+++ b/tests/integration/f3_test.go
@@ -4,14 +4,20 @@ package integration
 
 import (
 	"context"
+	"fmt"
+	"net/http"
 	"net/url"
 	"testing"
 
 	auth_model "code.gitea.io/gitea/models/auth"
+	"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/test"
 	"code.gitea.io/gitea/services/f3/util"
+	"code.gitea.io/gitea/tests"
 
+	"github.com/markbates/goth"
 	"github.com/stretchr/testify/assert"
 	"lab.forgefriends.org/friendlyforgeformat/gof3"
 	f3_forges "lab.forgefriends.org/friendlyforgeformat/gof3/forges"
@@ -115,3 +121,60 @@ func TestF3(t *testing.T) {
 		//		f3_util.Command(context.Background(), "cp", "-a", f3.GetDirectory(), "abc")
 	})
 }
+
+func TestMaybePromoteF3User(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	//
+	// OAuth2 authentication source GitLab
+	//
+	gitlabName := "gitlab"
+	_ = addAuthSource(t, authSourcePayloadGitLabCustom(gitlabName))
+	//
+	// F3 authentication source matching the GitLab authentication source
+	//
+	f3Name := "f3"
+	f3 := createF3AuthSource(t, f3Name, "http://mygitlab.eu", gitlabName)
+
+	//
+	// Create a user as if it had been previously been created by the F3
+	// authentication source.
+	//
+	gitlabUserID := "5678"
+	gitlabEmail := "gitlabuser@example.com"
+	userBeforeSignIn := &user_model.User{
+		Name:        "gitlabuser",
+		Type:        user_model.UserTypeRemoteUser,
+		LoginType:   auth_model.F3,
+		LoginSource: f3.ID,
+		LoginName:   gitlabUserID,
+	}
+	defer createUser(context.Background(), t, userBeforeSignIn)()
+
+	//
+	// A request for user information sent to Goth will return a
+	// goth.User exactly matching the user created above.
+	//
+	defer mockCompleteUserAuth(func(res http.ResponseWriter, req *http.Request) (goth.User, error) {
+		return goth.User{
+			Provider: gitlabName,
+			UserID:   gitlabUserID,
+			Email:    gitlabEmail,
+		}, nil
+	})()
+	req := NewRequest(t, "GET", fmt.Sprintf("/user/oauth2/%s/callback?code=XYZ&state=XYZ", gitlabName))
+	resp := MakeRequest(t, req, http.StatusSeeOther)
+	assert.Equal(t, "/", test.RedirectURL(resp))
+	userAfterSignIn := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: userBeforeSignIn.ID})
+
+	// both are about the same user
+	assert.Equal(t, userAfterSignIn.ID, userBeforeSignIn.ID)
+	// the login time was updated, proof the login succeeded
+	assert.Greater(t, userAfterSignIn.LastLoginUnix, userBeforeSignIn.LastLoginUnix)
+	// the login type was promoted from F3 to OAuth2
+	assert.Equal(t, userBeforeSignIn.LoginType, auth_model.F3)
+	assert.Equal(t, userAfterSignIn.LoginType, auth_model.OAuth2)
+	// the OAuth2 email was used to set the missing user email
+	assert.Equal(t, userBeforeSignIn.Email, "")
+	assert.Equal(t, userAfterSignIn.Email, gitlabEmail)
+}
diff --git a/tests/integration/integration_test.go b/tests/integration/integration_test.go
index a25d36575e..41f29b1aa1 100644
--- a/tests/integration/integration_test.go
+++ b/tests/integration/integration_test.go
@@ -35,6 +35,7 @@ import (
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	"code.gitea.io/gitea/routers"
+	"code.gitea.io/gitea/services/auth/source/f3"
 	"code.gitea.io/gitea/services/auth/source/oauth2"
 	user_service "code.gitea.io/gitea/services/user"
 	"code.gitea.io/gitea/tests"
@@ -294,6 +295,21 @@ func authSourcePayloadOIDC(name string) map[string]string {
 	return payload
 }
 
+func createF3AuthSource(t *testing.T, name, url, matchingSource string) *auth.Source {
+	assert.NoError(t, auth.CreateSource(&auth.Source{
+		Type:     auth.F3,
+		Name:     name,
+		IsActive: true,
+		Cfg: &f3.Source{
+			URL:            url,
+			MatchingSource: matchingSource,
+		},
+	}))
+	source, err := auth.GetSourceByName(context.Background(), name)
+	assert.NoError(t, err)
+	return source
+}
+
 func createUser(ctx context.Context, t testing.TB, user *user_model.User) func() {
 	user.MustChangePassword = false
 	user.LowerName = strings.ToLower(user.Name)