Record OAuth client type at registration (#21316)

The OAuth spec [defines two types of
client](https://datatracker.ietf.org/doc/html/rfc6749#section-2.1),
confidential and public. Previously Gitea assumed all clients to be
confidential.

> OAuth defines two client types, based on their ability to authenticate
securely with the authorization server (i.e., ability to
>   maintain the confidentiality of their client credentials):
>
>   confidential
> Clients capable of maintaining the confidentiality of their
credentials (e.g., client implemented on a secure server with
> restricted access to the client credentials), or capable of secure
client authentication using other means.
>
>   **public
> Clients incapable of maintaining the confidentiality of their
credentials (e.g., clients executing on the device used by the resource
owner, such as an installed native application or a web browser-based
application), and incapable of secure client authentication via any
other means.**
>
> The client type designation is based on the authorization server's
definition of secure authentication and its acceptable exposure levels
of client credentials. The authorization server SHOULD NOT make
assumptions about the client type.

 https://datatracker.ietf.org/doc/html/rfc8252#section-8.4

> Authorization servers MUST record the client type in the client
registration details in order to identify and process requests
accordingly.

Require PKCE for public clients:
https://datatracker.ietf.org/doc/html/rfc8252#section-8.1

> Authorization servers SHOULD reject authorization requests from native
apps that don't use PKCE by returning an error message

Fixes #21299

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

4 files changed, 68 insertions, 0 deletions

diff --git a/models/migrations/fixtures/Test_addConfidentialClientColumnToOAuth2ApplicationTable/o_auth2_application.yml b/models/migrations/fixtures/Test_addConfidentialClientColumnToOAuth2ApplicationTable/o_auth2_application.yml
new file mode 100644
index 0000000000..a88c2ef89f
--- /dev/null
+++ b/models/migrations/fixtures/Test_addConfidentialClientColumnToOAuth2ApplicationTable/o_auth2_application.yml
@@ -0,0 +1,2 @@
+-
+  id: 1
diff --git a/models/migrations/migrations.go b/models/migrations/migrations.go
index cca6c52d42..a6201c1090 100644
--- a/models/migrations/migrations.go
+++ b/models/migrations/migrations.go
@@ -421,6 +421,8 @@ var migrations = []Migration{
 	NewMigration("Add TeamInvite table", addTeamInviteTable),
 	// v229 -> v230
 	NewMigration("Update counts of all open milestones", updateOpenMilestoneCounts),
+	// v230 -> v231
+	NewMigration("Add ConfidentialClient column (default true) to OAuth2Application table", addConfidentialClientColumnToOAuth2ApplicationTable),
 }
 
 // GetCurrentDBVersion returns the current db version
diff --git a/models/migrations/v230.go b/models/migrations/v230.go
new file mode 100644
index 0000000000..f08e6a3764
--- /dev/null
+++ b/models/migrations/v230.go
@@ -0,0 +1,18 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"xorm.io/xorm"
+)
+
+// addConfidentialColumnToOAuth2ApplicationTable: add ConfidentialClient column, setting existing rows to true
+func addConfidentialClientColumnToOAuth2ApplicationTable(x *xorm.Engine) error {
+	type OAuth2Application struct {
+		ConfidentialClient bool `xorm:"NOT NULL DEFAULT TRUE"`
+	}
+
+	return x.Sync(new(OAuth2Application))
+}
diff --git a/models/migrations/v230_test.go b/models/migrations/v230_test.go
new file mode 100644
index 0000000000..98ba3f5d97
--- /dev/null
+++ b/models/migrations/v230_test.go
@@ -0,0 +1,46 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_addConfidentialClientColumnToOAuth2ApplicationTable(t *testing.T) {
+	// premigration
+	type OAuth2Application struct {
+		ID int64
+	}
+
+	// Prepare and load the testing database
+	x, deferable := prepareTestEnv(t, 0, new(OAuth2Application))
+	defer deferable()
+	if x == nil || t.Failed() {
+		return
+	}
+
+	if err := addConfidentialClientColumnToOAuth2ApplicationTable(x); err != nil {
+		assert.NoError(t, err)
+		return
+	}
+
+	// postmigration
+	type ExpectedOAuth2Application struct {
+		ID                 int64
+		ConfidentialClient bool
+	}
+
+	got := []ExpectedOAuth2Application{}
+	if err := x.Table("o_auth2_application").Select("id, confidential_client").Find(&got); !assert.NoError(t, err) {
+		return
+	}
+
+	assert.NotEmpty(t, got)
+	for _, e := range got {
+		assert.True(t, e.ConfidentialClient)
+	}
+}