From d841e95191ddcc04a06dbf022a6b06884bf2bee6 Mon Sep 17 00:00:00 2001
From: Zettat123 <zettat123@gmail.com>
Date: Mon, 20 May 2024 15:17:00 +0800
Subject: [PATCH] Return `access_denied` error when an OAuth2 request is denied
 (#30974)

According to [RFC
6749](https://datatracker.ietf.org/doc/html/rfc6749#section-4.1.2.1),
when the resource owner or authorization server denied an request, an
`access_denied` error should be returned. But currently in this case
Gitea does not return any error.

For example, if the user clicks "Cancel" here, an `access_denied` error
should be returned.

<img width="360px"
src="https://github.com/go-gitea/gitea/assets/15528715/be31c09b-4c0a-4701-b7a4-f54b8fe3a6c5"
/>

(cherry picked from commit f1d9f18d96050d89a4085c961f572f07b1e653d1)
(cherry picked from commit 886a675f62233dcde3ac0d7b2181484f29344f26)
---
 routers/web/auth/oauth.go      | 10 ++++++++++
 services/forms/user_form.go    |  1 +
 templates/user/auth/grant.tmpl |  4 ++--
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/routers/web/auth/oauth.go b/routers/web/auth/oauth.go
index f5ca0bda5e..73fcd5524d 100644
--- a/routers/web/auth/oauth.go
+++ b/routers/web/auth/oauth.go
@@ -539,6 +539,16 @@ func GrantApplicationOAuth(ctx *context.Context) {
 		ctx.Error(http.StatusBadRequest)
 		return
 	}
+
+	if !form.Granted {
+		handleAuthorizeError(ctx, AuthorizeError{
+			State:            form.State,
+			ErrorDescription: "the request is denied",
+			ErrorCode:        ErrorCodeAccessDenied,
+		}, form.RedirectURI)
+		return
+	}
+
 	app, err := auth.GetOAuth2ApplicationByClientID(ctx, form.ClientID)
 	if err != nil {
 		ctx.ServerError("GetOAuth2ApplicationByClientID", err)
diff --git a/services/forms/user_form.go b/services/forms/user_form.go
index 4e603a3115..0b7bea4638 100644
--- a/services/forms/user_form.go
+++ b/services/forms/user_form.go
@@ -162,6 +162,7 @@ func (f *AuthorizationForm) Validate(req *http.Request, errs binding.Errors) bin
 // GrantApplicationForm form for authorizing oauth2 clients
 type GrantApplicationForm struct {
 	ClientID    string `binding:"Required"`
+	Granted     bool
 	RedirectURI string
 	State       string
 	Scope       string
diff --git a/templates/user/auth/grant.tmpl b/templates/user/auth/grant.tmpl
index cb9bba8749..a18a3bd27a 100644
--- a/templates/user/auth/grant.tmpl
+++ b/templates/user/auth/grant.tmpl
@@ -23,8 +23,8 @@
 					<input type="hidden" name="scope" value="{{.Scope}}">
 					<input type="hidden" name="nonce" value="{{.Nonce}}">
 					<input type="hidden" name="redirect_uri" value="{{.RedirectURI}}">
-					<button type="submit" id="authorize-app" value="{{ctx.Locale.Tr "auth.authorize_application"}}" class="ui red inline button">{{ctx.Locale.Tr "auth.authorize_application"}}</button>
-					<a href="{{.RedirectURI}}" class="ui basic primary inline button">Cancel</a>
+					<button type="submit" id="authorize-app" name="granted" value="true" class="ui red inline button">{{ctx.Locale.Tr "auth.authorize_application"}}</button>
+					<button type="submit" name="granted" value="false" class="ui basic primary inline button">{{ctx.Locale.Tr "cancel"}}</button>
 				</form>
 			</div>
 		</div>