override relative url

apps/login/src/app/login/route.ts

@@ -217,7 +217,7 @@ export async function GET(request: NextRequest) {
             params.set("organization", organization);
           }
 
-          const url = await startIdentityProviderFlow({
+          let url: string | null = await startIdentityProviderFlow({
             serviceUrl,
             idpId,
             urls: {
@@ -237,9 +237,12 @@ export async function GET(request: NextRequest) {
             );
           }
 
-          const absoluteUrl = constructUrl(request, url);
+          if (url.startsWith("/")) {
+            // if the url is a relative path, construct the absolute url
+            url = constructUrl(request, url).toString();
+          }
 
-          return NextResponse.redirect(absoluteUrl);
+          return NextResponse.redirect(url);
         }
       }
     }

apps/login/src/lib/zitadel.ts

@@ -985,16 +985,18 @@ export async function startIdentityProviderFlow({
         return resp.nextStep.value;
       } else if (resp.nextStep.case === "formData" && resp.nextStep.value) {
         const formData: FormData = resp.nextStep.value;
-        const redirectUrl = new URL("/saml-post");
+        const redirectUrl = "/saml-post";
+
+        const params = new URLSearchParams({ url: formData.url });
 
-        redirectUrl.searchParams.set("url", formData.url);
         Object.entries(formData.fields).forEach(([k, v]) => {
-          redirectUrl.searchParams.set(k, v);
+          params.append(k, v);
         });
 
-        return redirectUrl.toString();
+        return `${redirectUrl}?${params.toString()}`;
+      } else {
+        return null;
       }
-      return null;
     });
 }