Unify two factor check (#27915) (#27939)

Backport of #27915

Fixes #27819

We have support for two factor logins with the normal web login and with
basic auth. For basic auth the two factor check was implemented at three
different places and you need to know that this check is necessary. This
PR moves the check into the basic auth itself.

(cherry picked from commit 00705da102)

tests/integration/api_twofa_test.go

@@ -0,0 +1,54 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"net/http"
+	"testing"
+	"time"
+
+	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/tests"
+
+	"github.com/pquerna/otp/totp"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAPITwoFactor(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 16})
+
+	req := NewRequestf(t, "GET", "/api/v1/user")
+	req = AddBasicAuthHeader(req, user.Name)
+	MakeRequest(t, req, http.StatusOK)
+
+	otpKey, err := totp.Generate(totp.GenerateOpts{
+		SecretSize:  40,
+		Issuer:      "gitea-test",
+		AccountName: user.Name,
+	})
+	assert.NoError(t, err)
+
+	tfa := &auth_model.TwoFactor{
+		UID: user.ID,
+	}
+	assert.NoError(t, tfa.SetSecret(otpKey.Secret()))
+
+	assert.NoError(t, auth_model.NewTwoFactor(tfa))
+
+	req = NewRequestf(t, "GET", "/api/v1/user")
+	req = AddBasicAuthHeader(req, user.Name)
+	MakeRequest(t, req, http.StatusUnauthorized)
+
+	passcode, err := totp.GenerateCode(otpKey.Secret(), time.Now())
+	assert.NoError(t, err)
+
+	req = NewRequestf(t, "GET", "/api/v1/user")
+	req = AddBasicAuthHeader(req, user.Name)
+	req.Header.Set("X-Gitea-OTP", passcode)
+	MakeRequest(t, req, http.StatusOK)
+}