Entering to my app hosted on firebase hosting redirects to google login page

问题

Was tweaking with Server Side Rendering and google cloud functions. Deployed everything on hosting and something really strange happens. When I enter my page, https://accounts.google.com page appears...

with some really long link:

https://accounts.google.com/signin/v2/identifier?
 service=ah&passive=true&continue=https%3A%2F%2Fappengine.google.com
  %2F_ah%2Fconflogin%3Fcontinue%3Dhttps%3A%2F%2Fus-central1-treebase-
   b21-d5.cloudfunctions.net%2Fssrapp%2F&flowName=GlifWebSignIn&flowEntry=
    ServiceLogin&hl=en-GB

What may cause this? How to fix it? Thanks!

`index.js` file responsible for SSR:

import React from 'react';
import { renderToString } from 'react-dom/server';
import express from 'express';
import App from './app/containers/App';
import functions from 'firebase-functions';

const app = express();

app.get('**', (req, res) => {
  const html = renderToString(<App />);
  res.set('Cache-Control', 'public, max-age=600, s-maxage=1200');
  res.send(`
    <!doctype html>
    <html lang="en">
      <head>
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
      </head>

      <body>
        <div id="app">${html}</div>
        <div id="fb-root"></div>
        <script type="text/javascript" src="/main.30e39d69fe1ce70d8983.js"></script>
      </body>
    </html>
  `);
});

export const ssrapp = functions.https.onRequest(app);

`firebase.json`

{
  "hosting": {
    "public": "build",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ],
    "rewrites": [
      {
        "source": "**",
        "function": "ssrapp"
      }
    ]
  }
}