fix: callback URL validation not validated if prompt=none

backend/internal/controller/oidc_controller.go

@@ -32,6 +32,7 @@ func NewOidcController(group *gin.RouterGroup, authMiddleware *middleware.AuthMi
 	}
 
 	group.POST("/oidc/authorize", authMiddleware.WithAdminNotRequired().Add(), oc.authorizeHandler)
+	group.POST("/oidc/authorize/callback-url", oc.authorizeCallbackURLHandler)
 	group.POST("/oidc/authorization-required", authMiddleware.WithAdminNotRequired().Add(), oc.authorizationConfirmationRequiredHandler)
 	group.GET("/oidc/par-request-info", authMiddleware.WithAdminNotRequired().Add(), oc.parRequestInfoHandler)
 
@@ -111,6 +112,7 @@ func (oc *OidcController) authorizeHandler(c *gin.Context) {
 			c.JSON(http.StatusOK, gin.H{
 				"error":            err.Error(),
 				"requiresRedirect": true,
+				"callbackURL":      callbackURL,
 			})
 			return
 		}
@@ -127,6 +129,36 @@ func (oc *OidcController) authorizeHandler(c *gin.Context) {
 	c.JSON(http.StatusOK, response)
 }
 
+// authorizeCallbackURLHandler godoc
+// @Summary Resolve a validated callback URL for an OIDC authorization request
+// @Description Resolves the redirect URI against the client's configured callback URLs without consuming PAR records.
+// @Tags OIDC
+// @Accept json
+// @Produce json
+// @Param request body dto.AuthorizeOidcClientCallbackRequestDto true "Authorization callback parameters"
+// @Success 200 {object} dto.AuthorizeOidcClientCallbackResponseDto "Resolved callback URL"
+// @Router /api/oidc/authorize/callback-url [post]
+func (oc *OidcController) authorizeCallbackURLHandler(c *gin.Context) {
+	var input dto.AuthorizeOidcClientCallbackRequestDto
+	if err := c.ShouldBindJSON(&input); err != nil {
+		_ = c.Error(err)
+		return
+	}
+
+	callbackURL, err := oc.oidcService.ResolveAuthorizeCallbackURL(
+		c.Request.Context(),
+		input.ClientID,
+		input.CallbackURL,
+		input.RequestURI,
+	)
+	if err != nil {
+		_ = c.Error(err)
+		return
+	}
+
+	c.JSON(http.StatusOK, dto.AuthorizeOidcClientCallbackResponseDto{CallbackURL: callbackURL})
+}
+
 // isOidcPromptError checks if an error is a prompt-related OIDC error that should trigger a redirect
 func isOidcPromptError(err error) bool {
 	var loginReq *common.OidcLoginRequiredError

backend/internal/dto/oidc_dto.go

@@ -105,6 +105,16 @@ type AuthorizeOidcClientResponseDto struct {
 	Issuer      string `json:"issuer"`
 }
 
+type AuthorizeOidcClientCallbackRequestDto struct {
+	ClientID    string `json:"clientID" binding:"required"`
+	CallbackURL string `json:"callbackURL"`
+	RequestURI  string `json:"requestURI"`
+}
+
+type AuthorizeOidcClientCallbackResponseDto struct {
+	CallbackURL string `json:"callbackURL"`
+}
+
 type AuthorizationRequiredDto struct {
 	ClientID   string `json:"clientID" binding:"required"`
 	Scope      string `json:"scope"`

backend/internal/service/oidc_service.go

@@ -216,7 +216,7 @@ func (s *OidcService) Authorize(ctx context.Context, input dto.AuthorizeOidcClie
 			return "", "", err
 		}
 		if !hasAlreadyAuthorized {
-			return "", "", &common.OidcConsentRequiredError{}
+			return "", callbackURL, &common.OidcConsentRequiredError{}
 		}
 	}
 
@@ -820,7 +820,41 @@ func (s *OidcService) ResolveAllowedCallbackURL(ctx context.Context, clientID, i
 		return "", err
 	}
 
-	if inputCallbackURL == "" || len(client.CallbackURLs) == 0 {
+	return resolveConfiguredCallbackURL(&client, inputCallbackURL)
+}
+
+// ResolveAuthorizeCallbackURL resolves the callback URL for a browser authorization
+// request without authorizing the user or consuming PAR state.
+func (s *OidcService) ResolveAuthorizeCallbackURL(ctx context.Context, clientID, inputCallbackURL, requestURI string) (string, error) {
+	client, err := s.GetClient(ctx, clientID)
+	if err != nil {
+		return "", err
+	}
+
+	if client.RequiresPushedAuthorizationRequests && requestURI == "" {
+		return "", &common.OidcPARRequiredError{}
+	}
+
+	if requestURI != "" {
+		par, err := s.GetPushedAuthorizationRequest(ctx, clientID, requestURI)
+		if err != nil {
+			return "", err
+		}
+		inputCallbackURL = par.Parameters.RedirectURI
+	}
+
+	return resolveConfiguredCallbackURL(&client, inputCallbackURL)
+}
+
+func resolveConfiguredCallbackURL(client *model.OidcClient, inputCallbackURL string) (string, error) {
+	if inputCallbackURL == "" {
+		if len(client.CallbackURLs) > 0 {
+			return client.CallbackURLs[0], nil
+		}
+		return "", &common.OidcMissingCallbackURLError{}
+	}
+
+	if len(client.CallbackURLs) == 0 {
 		return "", &common.OidcMissingCallbackURLError{}
 	}