From 8b379b7466ea6a3cb2f9d91b28c16d450f6a5987 Mon Sep 17 00:00:00 2001
From: kolaente <k@knt.li>
Date: Thu, 26 Mar 2026 16:32:01 +0100
Subject: [PATCH] feat: add OAuth 2.0 authorize endpoint

Add POST /api/v1/oauth/authorize behind auth middleware. Validates
OAuth parameters (response_type, redirect_uri, PKCE), fetches the
authenticated user, creates an authorization code, and returns it
as JSON for the frontend to handle the redirect.
---
 pkg/modules/auth/oauth2server/authorize.go | 100 +++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 pkg/modules/auth/oauth2server/authorize.go

diff --git a/pkg/modules/auth/oauth2server/authorize.go b/pkg/modules/auth/oauth2server/authorize.go
new file mode 100644
index 000000000..873c00900
--- /dev/null
+++ b/pkg/modules/auth/oauth2server/authorize.go
@@ -0,0 +1,100 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package oauth2server
+
+import (
+	"net/http"
+
+	"code.vikunja.io/api/pkg/db"
+	"code.vikunja.io/api/pkg/models"
+	"code.vikunja.io/api/pkg/user"
+
+	"github.com/labstack/echo/v5"
+)
+
+// authorizeRequest represents the JSON body for the authorize endpoint.
+type authorizeRequest struct {
+	ResponseType        string `json:"response_type"`
+	ClientID            string `json:"client_id"`
+	RedirectURI         string `json:"redirect_uri"`
+	State               string `json:"state"`
+	CodeChallenge       string `json:"code_challenge"`
+	CodeChallengeMethod string `json:"code_challenge_method"`
+}
+
+// AuthorizeResponse is returned on successful authorization code creation.
+type AuthorizeResponse struct {
+	Code        string `json:"code"`
+	RedirectURI string `json:"redirect_uri"`
+	State       string `json:"state"`
+}
+
+// HandleAuthorize handles POST /oauth/authorize.
+// It validates the OAuth parameters, creates an authorization code, and
+// returns it as JSON. Authentication is handled by the token middleware.
+func HandleAuthorize(c *echo.Context) error {
+	var req authorizeRequest
+	if err := c.Bind(&req); err != nil {
+		return echo.NewHTTPError(http.StatusBadRequest, "Invalid request body")
+	}
+
+	// Validate response_type
+	if req.ResponseType != "code" {
+		return echo.NewHTTPError(http.StatusBadRequest, "response_type must be 'code'")
+	}
+
+	// Validate redirect_uri
+	if !ValidateRedirectURI(req.RedirectURI) {
+		return &models.ErrOAuthInvalidRedirectURI{}
+	}
+
+	// Validate PKCE (required)
+	if req.CodeChallenge == "" || req.CodeChallengeMethod != "S256" {
+		return &models.ErrOAuthMissingPKCE{}
+	}
+
+	// Get the authenticated user from the middleware
+	u, err := user.GetCurrentUser(c)
+	if err != nil {
+		return err
+	}
+
+	s := db.NewSession()
+	defer s.Close()
+
+	fullUser, err := user.GetUserByID(s, u.ID)
+	if err != nil {
+		_ = s.Rollback()
+		return err
+	}
+
+	code, err := models.CreateOAuthCode(s, fullUser.ID, req.ClientID, req.RedirectURI, req.CodeChallenge, req.CodeChallengeMethod)
+	if err != nil {
+		_ = s.Rollback()
+		return err
+	}
+
+	if err := s.Commit(); err != nil {
+		return err
+	}
+
+	return c.JSON(http.StatusOK, AuthorizeResponse{
+		Code:        code,
+		RedirectURI: req.RedirectURI,
+		State:       req.State,
+	})
+}