Minimal OpenID Connect implementation

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

Author: ojohnny

docs/content/doc/developers/oauth2-provider.md

@@ -30,7 +30,9 @@ Gitea supports acting as an OAuth2 provider to allow third party applications to
 
 ## Supported OAuth2 Grants
 
-At the moment Gitea only supports the [**Authorization Code Grant**](https://tools.ietf.org/html/rfc6749#section-1.3.1) standard with additional support of the [Proof Key for Code Exchange (PKCE)](https://tools.ietf.org/html/rfc7636) extension.
+At the moment Gitea only supports the [**Authorization Code Grant**](https://tools.ietf.org/html/rfc6749#section-1.3.1) standard with additional support of the following extensions:
+- [Proof Key for Code Exchange (PKCE)](https://tools.ietf.org/html/rfc7636)
+- [OpenID Connect (OIDC)](https://openid.net/specs/openid-connect-core-1_0.html#CodeFlowAuth)
 
 To use the Authorization Code Grant as a third party application it is required to register a new application via the "Settings" (`/user/settings/applications`) section of the settings.
 

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)

modules/auth/user_form.go

@@ -147,6 +147,8 @@ type AuthorizationForm struct {
 	ClientID     string `binding:"Required"`
 	RedirectURI  string
 	State        string
+	Scope        string
+	Nonce        string
 
 	// PKCE support
 	CodeChallengeMethod string // S256, plain
@@ -163,6 +165,8 @@ type GrantApplicationForm struct {
 	ClientID    string `binding:"Required"`
 	RedirectURI string
 	State       string
+	Scope       string
+	Nonce       string
 }
 
 // Validate validates the fields

routers/user/oauth.go

@@ -107,9 +107,10 @@ type AccessTokenResponse struct {
 	TokenType    TokenType `json:"token_type"`
 	ExpiresIn    int64     `json:"expires_in"`
 	RefreshToken string    `json:"refresh_token"`
+	IDToken      string    `json:"id_token,omitempty"`
 }
 
-func newAccessTokenResponse(grant *models.OAuth2Grant) (*AccessTokenResponse, *AccessTokenError) {
+func newAccessTokenResponse(grant *models.OAuth2Grant, clientSecret string) (*AccessTokenResponse, *AccessTokenError) {
 	if setting.OAuth2.InvalidateRefreshTokens {
 		if err := grant.IncreaseCounter(); err != nil {
 			return nil, &AccessTokenError{
@@ -153,11 +154,40 @@ func newAccessTokenResponse(grant *models.OAuth2Grant) (*AccessTokenResponse, *A
 		}
 	}
 
+	// generate OpenID Connect id_token
+	signedIDToken := ""
+	if grant.ScopeContains("openid") {
+		app, err := models.GetOAuth2ApplicationByID(grant.ApplicationID)
+		if err != nil {
+			return nil, &AccessTokenError{
+				ErrorCode:        AccessTokenErrorCodeInvalidRequest,
+				ErrorDescription: "cannot find application",
+			}
+		}
+		idToken := &models.OIDCToken{
+			StandardClaims: jwt.StandardClaims{
+				ExpiresAt: expirationDate.AsTime().Unix(),
+				Issuer:    setting.AppURL,
+				Audience:  app.ClientID,
+				Subject:   fmt.Sprint(grant.UserID),
+			},
+			Nonce: grant.Nonce,
+		}
+		signedIDToken, err = idToken.SignToken(clientSecret)
+		if err != nil {
+			return nil, &AccessTokenError{
+				ErrorCode:        AccessTokenErrorCodeInvalidRequest,
+				ErrorDescription: "cannot sign token",
+			}
+		}
+	}
+
 	return &AccessTokenResponse{
 		AccessToken:  signedAccessToken,
 		TokenType:    TokenTypeBearer,
 		ExpiresIn:    setting.OAuth2.AccessTokenExpirationTime,
 		RefreshToken: signedRefreshToken,
+		IDToken:      signedIDToken,
 	}, nil
 }
 
@@ -264,6 +294,13 @@ func AuthorizeOAuth(ctx *context.Context, form auth.AuthorizationForm) {
 			handleServerError(ctx, form.State, form.RedirectURI)
 			return
 		}
+		// Update nonce to reflect the new session
+		if len(form.Nonce) > 0 {
+			err := grant.SetNonce(form.Nonce)
+			if err != nil {
+				log.Error("Unable to update nonce: %v", err)
+			}
+		}
 		ctx.Redirect(redirect.String(), 302)
 		return
 	}
@@ -272,6 +309,8 @@ func AuthorizeOAuth(ctx *context.Context, form auth.AuthorizationForm) {
 	ctx.Data["Application"] = app
 	ctx.Data["RedirectURI"] = form.RedirectURI
 	ctx.Data["State"] = form.State
+	ctx.Data["Scope"] = form.Scope
+	ctx.Data["Nonce"] = form.Nonce
 	ctx.Data["ApplicationUserLink"] = "<a href=\"" + html.EscapeString(setting.AppURL) + html.EscapeString(url.PathEscape(app.User.LowerName)) + "\">@" + html.EscapeString(app.User.Name) + "</a>"
 	ctx.Data["ApplicationRedirectDomainHTML"] = "<strong>" + html.EscapeString(form.RedirectURI) + "</strong>"
 	// TODO document SESSION <=> FORM
@@ -313,7 +352,7 @@ func GrantApplicationOAuth(ctx *context.Context, form auth.GrantApplicationForm)
 		ctx.ServerError("GetOAuth2ApplicationByClientID", err)
 		return
 	}
-	grant, err := app.CreateGrant(ctx.User.ID)
+	grant, err := app.CreateGrant(ctx.User.ID, form.Scope)
 	if err != nil {
 		handleAuthorizeError(ctx, AuthorizeError{
 			State:            form.State,
@@ -322,6 +361,12 @@ func GrantApplicationOAuth(ctx *context.Context, form auth.GrantApplicationForm)
 		}, form.RedirectURI)
 		return
 	}
+	if len(form.Nonce) > 0 {
+		err := grant.SetNonce(form.Nonce)
+		if err != nil {
+			log.Error("Unable to update nonce: %v", err)
+		}
+	}
 
 	var codeChallenge, codeChallengeMethod string
 	codeChallenge, _ = ctx.Session.Get("CodeChallenge").(string)
@@ -409,7 +454,7 @@ func handleRefreshToken(ctx *context.Context, form auth.AccessTokenForm) {
 		log.Warn("A client tried to use a refresh token for grant_id = %d was used twice!", grant.ID)
 		return
 	}
-	accessToken, tokenErr := newAccessTokenResponse(grant)
+	accessToken, tokenErr := newAccessTokenResponse(grant, form.ClientSecret)
 	if tokenErr != nil {
 		handleAccessTokenError(ctx, *tokenErr)
 		return
@@ -471,7 +516,7 @@ func handleAuthorizationCode(ctx *context.Context, form auth.AccessTokenForm) {
 			ErrorDescription: "cannot proceed your request",
 		})
 	}
-	resp, tokenErr := newAccessTokenResponse(authorizationCode.Grant)
+	resp, tokenErr := newAccessTokenResponse(authorizationCode.Grant, form.ClientSecret)
 	if tokenErr != nil {
 		handleAccessTokenError(ctx, *tokenErr)
 		return

templates/user/auth/grant.tmpl

@@ -20,6 +20,8 @@
 					{{.CsrfTokenHtml}}
 					<input type="hidden" name="client_id" value="{{.Application.ClientID}}">
 					<input type="hidden" name="state" value="{{.State}}">
+					<input type="hidden" name="scope" value="{{.Scope}}">
+					<input type="hidden" name="nonce" value="{{.Nonce}}">
 					<input type="hidden" name="redirect_uri" value="{{.RedirectURI}}">
 					<input type="submit" id="authorize-app" value="{{.i18n.Tr "auth.authorize_application"}}" class="ui red inline button"/>
 					<a href="{{.RedirectURI}}" class="ui basic primary inline button">Cancel</a>