Stop sending scope on the authorization code token request (#579)

plugins/auth-oauth2/src/fetchAccessToken.ts

@@ -31,7 +31,13 @@ export async function fetchAccessToken(
     ],
   };
 
-  if (scope) httpRequest.body?.form.push({ name: "scope", value: scope });
+  // RFC 6749 §4.1.3 doesn't define scope for the authorization code token
+  // request, so strict servers (OpenIddict) reject it outright. Scope belongs on
+  // the authorize request, which already sends it. Every other grant does define
+  // it: §4.3.2 password, §4.4.2 client credentials, §6 refresh.
+  if (scope && grantType !== "authorization_code") {
+    httpRequest.body?.form.push({ name: "scope", value: scope });
+  }
   if (audience) httpRequest.body?.form.push({ name: "audience", value: audience });
 
   if ("clientAssertion" in args) {

plugins/auth-oauth2/tests/fetchAccessToken.test.ts

@@ -0,0 +1,93 @@
+import type { HttpRequest } from "@yaakapp/api";
+import { describe, expect, test } from "vite-plus/test";
+import { fetchAccessToken } from "../src/fetchAccessToken";
+
+/**
+ * Captures the request handed to ctx.httpRequest.send so tests can assert on the
+ * form body, and replies with a minimal successful token response.
+ */
+function createMockContext() {
+  const sent: Partial<HttpRequest>[] = [];
+
+  const ctx = {
+    httpRequest: {
+      async send({ httpRequest }: { httpRequest: Partial<HttpRequest> }) {
+        sent.push(httpRequest);
+        return {
+          httpResponse: { status: 200, error: null },
+          body: {
+            async text() {
+              return JSON.stringify({ access_token: "token-123" });
+            },
+          },
+        };
+      },
+    },
+  } as never;
+
+  return { ctx, sent };
+}
+
+function formNames(httpRequest: Partial<HttpRequest>) {
+  return (httpRequest.body?.form ?? []).map((p: { name: string }) => p.name);
+}
+
+function formValue(httpRequest: Partial<HttpRequest>, name: string) {
+  return (httpRequest.body?.form ?? []).find((p: { name: string }) => p.name === name)?.value;
+}
+
+const baseArgs = {
+  clientId: "client-123",
+  accessTokenUrl: "https://auth.example.com/token",
+  scope: "openid profile",
+  audience: null,
+  clientSecret: "secret",
+  credentialsInBody: true,
+  params: [],
+};
+
+describe("fetchAccessToken scope handling", () => {
+  test("omits scope for the authorization code grant", async () => {
+    const { ctx, sent } = createMockContext();
+
+    await fetchAccessToken(ctx, {
+      ...baseArgs,
+      grantType: "authorization_code",
+      params: [{ name: "code", value: "abc" }],
+    });
+
+    expect(formNames(sent[0]!)).not.toContain("scope");
+    // The rest of the request is untouched
+    expect(formValue(sent[0]!, "grant_type")).toBe("authorization_code");
+    expect(formValue(sent[0]!, "code")).toBe("abc");
+  });
+
+  test("sends scope for the client credentials grant", async () => {
+    const { ctx, sent } = createMockContext();
+
+    await fetchAccessToken(ctx, { ...baseArgs, grantType: "client_credentials" });
+
+    expect(formValue(sent[0]!, "scope")).toBe("openid profile");
+  });
+
+  test("sends scope for the password grant", async () => {
+    const { ctx, sent } = createMockContext();
+
+    await fetchAccessToken(ctx, { ...baseArgs, grantType: "password" });
+
+    expect(formValue(sent[0]!, "scope")).toBe("openid profile");
+  });
+
+  test("still sends audience for the authorization code grant", async () => {
+    const { ctx, sent } = createMockContext();
+
+    await fetchAccessToken(ctx, {
+      ...baseArgs,
+      grantType: "authorization_code",
+      audience: "https://api.example.com",
+    });
+
+    expect(formValue(sent[0]!, "audience")).toBe("https://api.example.com");
+    expect(formNames(sent[0]!)).not.toContain("scope");
+  });
+});