feat: Blog about grant oauth proxy.

Author: asaf

blog/2021-09-19-grant-proxy.md

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+---
+slug: grant-oauth-proxy-with-crossid
+title: Using grant OAuth2 proxy with Crossid
+description: How to use grant OAuth2 nodejs proxy with Crossid.
+author: Asaf Shakarzy
+author_title: Core Team
+author_url: https://github.com/asaf
+tags: [oauth2, openid, nodejs, proxy]
+---
+
+import AddIntegration from "../src/components/AddIntegration.js";
+import AppUserAssignment from "../src/components/AssignUserToApp.mdx";
+
+[grant](https://github.com/simov/grant) is a nodejs OAuth proxy.
+
+With few lines of code, _grant_ can add oauth login support for any node.js app.
+
+For example, [Strapi](https://strapi.io/) uses _grant_ to authenticate users via Oauth2.
+
+This post explains how to use _grant_ to authenticate Crossid.
+
+## Init a new project
+
+```bash
+mkdir grant-crossid && cd grant-crossid
+npm -y init
+npm install grant express express-session
+```
+
+## Let crossid know about Grant
+
+We need to let Crossid know about our grant app.
+
+<AddIntegration name="Web App" steps={["Redirect URIs: http://localhost:3005/connect/crossid/callback"]}/>
+
+### Grant your user access to this app.
+
+<AppUserAssignment/>
+
+Save the _Client ID_ to the next deployment steps.
+
+## config.json
+
+```json {8-10}
+{
+  "defaults": {
+    "origin": "http://localhost:3005",
+    "transport": "session",
+    "state": true
+  },
+  "crossid": {
+    "subdomain": "acme",
+    "key": "<client_id>",
+    "secret": "<client_secret>",
+    "scope": ["openid"],
+    "callback": "/hello",
+    "response": ["tokens", "raw", "profile"]
+  }
+}
+```
+
+The configuration file defines the _crossid_ as an auth provider.
+
+- replace _subdomain_ with your [tenant](/docs/concepts/tenant).
+- replace _<client_id>_ and _<client_secret>_ with your app credentials.
+
+## index.js
+
+```js
+var express = require("express");
+var session = require("express-session");
+var grant = require("grant").express();
+
+express()
+  .use(session({ secret: "grant", saveUninitialized: true, resave: false }))
+  .use(grant(require("./config.json")))
+  .get("/hello", (req, res) => {
+    res.end(JSON.stringify(req.session.grant.response, null, 2));
+  })
+  .listen(3005);
+```
+
+## Try it
+
+Run the example by: `node index.js`
+
+Open browser in _https://localhost:3005/connect/crossid_
+
+You should be redirected to the login page, once user is logged in, you should see the _access token_ and the user's profile.
+
+## References
+
+- repo: https://github.com/simov/grant