feat: Add scope parameter to startAuthorization function

- Add optional scope parameter to startAuthorization function signature
- Include scope in authorization URL query parameters when provided
- Update auth function to pass through scope from provider.clientMetadata
- Add tests to verify scope is correctly included/excluded from auth URL

This enhancement allows clients to specify authorization scopes during the OAuth flow.

src/client/auth.test.ts

@@ -177,6 +177,31 @@ describe("OAuth Authorization", () => {
       expect(codeVerifier).toBe("test_verifier");
     });
 
+    it("includes scope parameter when provided", async () => {
+      const { authorizationUrl } = await startAuthorization(
+        "https://auth.example.com",
+        {
+          clientInformation: validClientInfo,
+          redirectUrl: "http://localhost:3000/callback",
+          scope: "read write profile",
+        }
+      );
+
+      expect(authorizationUrl.searchParams.get("scope")).toBe("read write profile");
+    });
+
+    it("excludes scope parameter when not provided", async () => {
+      const { authorizationUrl } = await startAuthorization(
+        "https://auth.example.com",
+        {
+          clientInformation: validClientInfo,
+          redirectUrl: "http://localhost:3000/callback",
+        }
+      );
+
+      expect(authorizationUrl.searchParams.has("scope")).toBe(false);
+    });
+
     it("uses metadata authorization_endpoint when provided", async () => {
       const { authorizationUrl } = await startAuthorization(
         "https://auth.example.com",