Add OAuth2 userinfo endpoint

routers/routes/web.go

@@ -395,6 +395,7 @@ func RegisterRoutes(m *web.Route) {
 	m.Any("/user/events", events.Events)
 
 	m.Group("/login/oauth", func() {
+		m.Get("/userinfo", user.InfoOAuth)
 		m.Get("/authorize", bindIgnErr(forms.AuthorizationForm{}), user.AuthorizeOAuth)
 		m.Post("/grant", bindIgnErr(forms.GrantApplicationForm{}), user.GrantApplicationOAuth)
 		// TODO manage redirection

routers/user/oauth_userinfo.go

@@ -0,0 +1,34 @@
+// Copyright 2021 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 user
+
+import (
+	"fmt"
+	"net/http"
+
+	"code.gitea.io/gitea/modules/context"
+)
+
+// userInfoResponse represents a successful userinfo response
+type userInfoResponse struct {
+	Sub      string `json:"sub"`
+	Name     string `json:"name"`
+	Username string `json:"preferred_username"`
+	Email    string `json:"email"`
+	Picture  string `json:"picture"`
+}
+
+// InfoOAuth responds with OAuth formatted userinfo
+func InfoOAuth(ctx *context.Context) {
+	user := ctx.User
+	response := &userInfoResponse{
+		Sub:      fmt.Sprint(user.ID),
+		Name:     user.FullName,
+		Username: user.Name,
+		Email:    user.Email,
+		Picture:  user.AvatarLink(),
+	}
+	ctx.JSON(http.StatusOK, response)
+}

templates/user/auth/oidc_wellknown.tmpl

@@ -2,6 +2,7 @@
     "issuer": "{{AppUrl | JSEscape | Safe}}",
     "authorization_endpoint": "{{AppUrl | JSEscape | Safe}}login/oauth/authorize",
     "token_endpoint": "{{AppUrl | JSEscape | Safe}}login/oauth/access_token",
+    "userinfo_endpoint": "{{AppUrl | JSEscape | Safe}}login/oauth/userinfo",
     "response_types_supported": [
         "code",
         "id_token"