how to access token on installation of the shopify app?

Question

I have been stuck at this point from 1month and im very disappointed, i am working on shopify with node js and i want to do it whenever someone will install my app i want to extract its access token and shop name and post it on another url below is my index.js file of back end provided from shopify app its latest version of the app. below is my code please do let me now how i can add some code and get access toke and shop name and post it anohter url or give me any reference site

    // @ts-check
    import { join } from "path";
    import { readFileSync } from "fs";
    import express from "express";
    import serveStatic from "serve-static";

    import shopify from "./shopify.js";
    import axios from "axios";
    import productCreator from "./product-creator.js";
    import GDPRWebhookHandlers from "./gdpr.js";

    const PORT = parseInt(process.env.BACKEND_PORT || process.env.PORT, 10);

    const STATIC_PATH =
      process.env.NODE_ENV === "production"
        ? `${process.cwd()}/frontend/dist`
        : `${process.cwd()}/frontend/`;

    const app = express();

    // Set up Shopify authentication and webhook handling
    app.get(shopify.config.auth.path, shopify.auth.begin());
    app.get(
      shopify.config.auth.callbackPath,
      shopify.auth.callback(),
      shopify.redirectToShopifyOrAppRoot()
    );
    app.post(
      shopify.config.webhooks.path,
      shopify.processWebhooks({ webhookHandlers: GDPRWebhookHandlers })
    );

    // All endpoints after this point will require an active session
    app.use("/api/*", shopify.validateAuthenticatedSession());

    app.use(express.json());

    app.get("/api/products/count", async (_req, res) => {
      const countData = await shopify.api.rest.Product.count({
        session: res.locals.shopify.session,
      });
      let tempData = [];
      tempData.push(countData);
      tempData.push(res.locals.shopify.session);
      res.status(200).send(tempData);
    });
    //....................//

    app.get("/api/products", async (req, res) => {
      try {
        // `session` is built as part of the OAuth process
        const session = res.locals.shopify.session;
        const client = new shopify.api.clients.Rest({ session });
        const product = await client.get({
          path: `products`,
        });
        // let tempData=[];
        // tempData.push(product);
        // tempData.push(res.locals.shopify.session)

        let tempData = {
          credentials: res.locals.shopify.session,
          product: product,
        };
        // console.log("INDExtempData",tempData)

        res.status(200).send(tempData);
      } catch (err) {
        res.status(500).send(err);
      }
    });

    //api for posting access_code
    app.get("/api/postToken", async (req, res) => {
      const data9 = {
        channel: "SHOPIFY",
        accessToken: "tokenTemp",
        storeName: "shopNameTemp",
      };

      try {
        const data1 = await axios.post(
          `https://0x7e9h042d.execute-api.eu-west-2.amazonaws.com/ingest`,

          data9,
          {
            headers: {
              Authorization:
                "eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxZDc2NmYyMi1mZGNjLTRhNTQtOTQ2OC00MzBlM2NlMDAxNmQiLCJleHAiOjE2Nzc5Nzc0NjMsImlhdCI6MTY3NjI0OTQ2M30.EEQeLzb4nxEBwBAszBQ9ZbPlSLzK2qnYguOKNWaSkMg",
              "realm-id": "772b9021-e740-42ff-9254-544b86aca440",
              "Content-Type": "application/json",
            },
          }
        );

        res.status(200).send(data1);
      } catch (err) {
        res.status(500).send(err);
      }
    });

    //////////
    // app.get(
    //   shopify.config.auth.callbackPath,
    //   shopify.auth.callback(),
    //   async (req, res) => {
    //     try {
    //       const accessToken = req.query.access_token;
    //       const shopName = req.query.shop;

    //       const data = {
    //         channel: "SHOPIFY",
    //         accessToken,
    //         storeName: shopName,
    //       };
    //       console.log("data", data);
    //       await axios.post(
    //         "https://0x7e9h042d.execute-api.eu-west-2.amazonaws.com/ingest",
    //         data,
    //         {
    //           headers: {
    //             Authorization:
    //               "Bearer eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxZDc2NmYyMi1mZGNjLTRhNTQtOTQ2OC00MzBlM2NlMDAxNmQiLCJleHAiOjE2Nzc5Nzc0NjMsImlhdCI6MTY3NjI0OTQ2M30.EEQeLzb4nxEBwBAszBQ9ZbPlSLzK2qnYguOKNWaSkMg",
    //             "realm-id": "772b9021-e740-42ff-9254-544b86aca440",
    //             "Content-Type": "application/json",
    //           },
    //         }
    //       );

    //       res.redirect("/");
    //     } catch (err) {
    //       res.status(500).send(err);
    //     }
    //   }
    // );
    app.get(
      shopify.config.auth.callbackPath,
      shopify.auth.callback(),
      async (req, res) => {
        console.log("top 1")
        try {
          console.log("top 2")
          const { shop, access_token } = await shopify.auth.validateAuthCallback(req);
          // Send a POST request to the API endpoint with the shop name and access token
          const response = await axios.post("https://0x7e9h042d.execute-api.eu-west-2.amazonaws.com/ingest", {
            shop,
            access_token
          },
          {
            headers: {
              Authorization:
                "Bearer eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxZDc2NmYyMi1mZGNjLTRhNTQtOTQ2OC00MzBlM2NlMDAxNmQiLCJleHAiOjE2Nzc5Nzc0NjMsImlhdCI6MTY3NjI0OTQ2M30.EEQeLzb4nxEBwBAszBQ9ZbPlSLzK2qnYguOKNWaSkMg",
              "realm-id": "772b9021-e740-42ff-9254-544b86aca440",
              "Content-Type": "application/json",
            },
          }
          );
          console.log(response.data);
        } catch (err) {
          console.log("top 3")
          console.error(err);
        }
        res.redirect('/');
      }
    );
    //....................//

    app.get("/api/products/create", async (_req, res) => {
      let status = 200;
      let error = null;

      try {
        await productCreator(res.locals.shopify.session);
      } catch (e) {
        // console.log(`Failed to process products/create: ${e.message}`);
        status = 500;
        error = e.message;
      }
      res.status(status).send({ success: status === 200, error });
    });

    app.get("api/products/get", async (_req, res) => {
      try {
        const productId = "11235813213455";
        // `session` is built as part of the OAuth process
        const client = new shopify.clients.Rest({ session });
        const product = await client.get({
          path: `products`,
          query: { id: 1, title: "title", shop: "search-flow2" },
        });

        res.status(500).send(product);
      } catch (err) {
        res.status(500).send(err);
      }
    });

    app.use(serveStatic(STATIC_PATH, { index: false }));

    app.use("/*", shopify.ensureInstalledOnShop(), async (_req, res, _next) => {
      return res
        .status(200)
        .set("Content-Type", "text/html")
        .send(readFileSync(join(STATIC_PATH, "index.html")));
    });

    // app.get("/testApi", async (_req, res) => {

    //   try {

    //   } catch (e) {
    //     console.log(`Failed to process products/create:`);

    //   }
    //   res.status(200).send("its working");
    // });

    app.listen(PORT);