Minimal OpenID Connect implementation (#14139)

This is "minimal" in the sense that only the Authorization Code Flow
from OpenID Connect Core is implemented.  No discovery, no configuration
endpoint, and no user scope management.

OpenID Connect is an extension to the (already implemented) OAuth 2.0
protocol, and essentially an `id_token` JWT is added to the access token
endpoint response when using the Authorization Code Flow.  I also added
support for the "nonce" field since it is required to be used in the
id_token if the client decides to include it in its initial request.

In order to enable this extension an OAuth 2.0 scope containing
"openid" is needed. Other OAuth 2.0 requests should not be impacted by
this change.

This minimal implementation is enough to enable single sign-on (SSO)
for other sites, e.g. by using something like `mod_auth_openidc` to
only allow access to a CI server if a user has logged into Gitea.

Fixes: #1310

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>

models/fixtures/oauth2_grant.yml

@@ -2,5 +2,6 @@
   user_id: 1
   application_id: 1
   counter: 1
+  scope: "openid profile"
   created_unix: 1546869730
   updated_unix: 1546869730

models/migrations/migrations.go

@@ -271,6 +271,8 @@ var migrations = []Migration{
 	NewMigration("Convert webhook task type from int to string", convertWebhookTaskTypeToString),
 	// v163 -> v164
 	NewMigration("Convert topic name from 25 to 50", convertTopicNameFrom25To50),
+	// v164 -> v165
+	NewMigration("Add scope and nonce columns to oauth2_grant table", addScopeAndNonceColumnsToOAuth2Grant),
 }
 
 // GetCurrentDBVersion returns the current db version

models/migrations/v164.go

@@ -0,0 +1,38 @@
+// Copyright 2020 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 (
+	"fmt"
+
+	"xorm.io/xorm"
+)
+
+// OAuth2Grant here is a snapshot of models.OAuth2Grant for this version
+// of the database, as it does not appear to have been added as a part
+// of a previous migration.
+type OAuth2Grant struct {
+	ID            int64  `xorm:"pk autoincr"`
+	UserID        int64  `xorm:"INDEX unique(user_application)"`
+	ApplicationID int64  `xorm:"INDEX unique(user_application)"`
+	Counter       int64  `xorm:"NOT NULL DEFAULT 1"`
+	Scope         string `xorm:"TEXT"`
+	Nonce         string `xorm:"TEXT"`
+	CreatedUnix   int64  `xorm:"created"`
+	UpdatedUnix   int64  `xorm:"updated"`
+}
+
+// TableName sets the database table name to be the correct one, as the
+// autogenerated table name for this struct is "o_auth2_grant".
+func (grant *OAuth2Grant) TableName() string {
+	return "oauth2_grant"
+}
+
+func addScopeAndNonceColumnsToOAuth2Grant(x *xorm.Engine) error {
+	if err := x.Sync2(new(OAuth2Grant)); err != nil {
+		return fmt.Errorf("Sync2: %v", err)
+	}
+	return nil
+}

models/oauth2_application.go

@@ -9,6 +9,7 @@ import (
 	"encoding/base64"
 	"fmt"
 	"net/url"
+	"strings"
 	"time"
 
 	"code.gitea.io/gitea/modules/secret"
@@ -103,14 +104,15 @@ func (app *OAuth2Application) getGrantByUserID(e Engine, userID int64) (grant *O
 }
 
 // CreateGrant generates a grant for an user
-func (app *OAuth2Application) CreateGrant(userID int64) (*OAuth2Grant, error) {
-	return app.createGrant(x, userID)
+func (app *OAuth2Application) CreateGrant(userID int64, scope string) (*OAuth2Grant, error) {
+	return app.createGrant(x, userID, scope)
 }
 
-func (app *OAuth2Application) createGrant(e Engine, userID int64) (*OAuth2Grant, error) {
+func (app *OAuth2Application) createGrant(e Engine, userID int64, scope string) (*OAuth2Grant, error) {
 	grant := &OAuth2Grant{
 		ApplicationID: app.ID,
 		UserID:        userID,
+		Scope:         scope,
 	}
 	_, err := e.Insert(grant)
 	if err != nil {
@@ -380,6 +382,8 @@ type OAuth2Grant struct {
 	Application   *OAuth2Application `xorm:"-"`
 	ApplicationID int64              `xorm:"INDEX unique(user_application)"`
 	Counter       int64              `xorm:"NOT NULL DEFAULT 1"`
+	Scope         string             `xorm:"TEXT"`
+	Nonce         string             `xorm:"TEXT"`
 	CreatedUnix   timeutil.TimeStamp `xorm:"created"`
 	UpdatedUnix   timeutil.TimeStamp `xorm:"updated"`
 }
@@ -431,6 +435,30 @@ func (grant *OAuth2Grant) increaseCount(e Engine) error {
 	return nil
 }
 
+// ScopeContains returns true if the grant scope contains the specified scope
+func (grant *OAuth2Grant) ScopeContains(scope string) bool {
+	for _, currentScope := range strings.Split(grant.Scope, " ") {
+		if scope == currentScope {
+			return true
+		}
+	}
+	return false
+}
+
+// SetNonce updates the current nonce value of a grant
+func (grant *OAuth2Grant) SetNonce(nonce string) error {
+	return grant.setNonce(x, nonce)
+}
+
+func (grant *OAuth2Grant) setNonce(e Engine, nonce string) error {
+	grant.Nonce = nonce
+	_, err := e.ID(grant.ID).Cols("nonce").Update(grant)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 // GetOAuth2GrantByID returns the grant with the given ID
 func GetOAuth2GrantByID(id int64) (*OAuth2Grant, error) {
 	return getOAuth2GrantByID(x, id)
@@ -533,3 +561,16 @@ func (token *OAuth2Token) SignToken() (string, error) {
 	jwtToken := jwt.NewWithClaims(jwt.SigningMethodHS512, token)
 	return jwtToken.SignedString(setting.OAuth2.JWTSecretBytes)
 }
+
+// OIDCToken represents an OpenID Connect id_token
+type OIDCToken struct {
+	jwt.StandardClaims
+	Nonce string `json:"nonce,omitempty"`
+}
+
+// SignToken signs an id_token with the (symmetric) client secret key
+func (token *OIDCToken) SignToken(clientSecret string) (string, error) {
+	token.IssuedAt = time.Now().Unix()
+	jwtToken := jwt.NewWithClaims(jwt.SigningMethodHS256, token)
+	return jwtToken.SignedString([]byte(clientSecret))
+}

models/oauth2_application_test.go

@@ -94,11 +94,12 @@ func TestOAuth2Application_GetGrantByUserID(t *testing.T) {
 func TestOAuth2Application_CreateGrant(t *testing.T) {
 	assert.NoError(t, PrepareTestDatabase())
 	app := AssertExistsAndLoadBean(t, &OAuth2Application{ID: 1}).(*OAuth2Application)
-	grant, err := app.CreateGrant(2)
+	grant, err := app.CreateGrant(2, "")
 	assert.NoError(t, err)
 	assert.NotNil(t, grant)
 	assert.Equal(t, int64(2), grant.UserID)
 	assert.Equal(t, int64(1), grant.ApplicationID)
+	assert.Equal(t, "", grant.Scope)
 }
 
 //////////////////// Grant
@@ -122,6 +123,15 @@ func TestOAuth2Grant_IncreaseCounter(t *testing.T) {
 	AssertExistsAndLoadBean(t, &OAuth2Grant{ID: 1, Counter: 2})
 }
 
+func TestOAuth2Grant_ScopeContains(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+	grant := AssertExistsAndLoadBean(t, &OAuth2Grant{ID: 1, Scope: "openid profile"}).(*OAuth2Grant)
+	assert.True(t, grant.ScopeContains("openid"))
+	assert.True(t, grant.ScopeContains("profile"))
+	assert.False(t, grant.ScopeContains("profil"))
+	assert.False(t, grant.ScopeContains("profile2"))
+}
+
 func TestOAuth2Grant_GenerateNewAuthorizationCode(t *testing.T) {
 	assert.NoError(t, PrepareTestDatabase())
 	grant := AssertExistsAndLoadBean(t, &OAuth2Grant{ID: 1}).(*OAuth2Grant)