feat: HMAC verification for web widget (#1643)

* feat: HMAC verification for web widget. Let you verify the authenticated contact via HMAC on the web widget to prevent data tampering.
* Add docs for identity-validation

Co-authored-by: Pranav Raj S <pranav@chatwoot.com>

docs/channels/identity-validation.md

@@ -0,0 +1,84 @@
+---
+path: '/docs/website-sdk/identity-validation'
+title: 'Identity validation in Chatwoot'
+---
+
+To make sure the conversations between the customers and the support agents are private and to disallow impersonation, you can setup identity validation Chatwoot.
+
+Identity validation can be enabled by generating an HMAC. The key used to generate HMAC for each webwidget is different and can be copied from Inboxes -> Settings -> Configuration -> Identity Validation -> Copy the token shown there
+
+You can generate HMAC in different languages as shown below.
+
+
+```php
+<?php
+
+$key = 'webwidget.hmac_token';
+$message = 'identifier';
+
+$identifier_hash = hash_hmac('sha256', $message, $key);
+?>
+```
+
+```js
+const crypto = require('crypto');
+
+const key = 'webwidget.hmac_token';
+const message = 'identifier';
+
+const hash = crypto.createHmac('sha256', key).update(message);
+
+hash.digest('hex');
+```
+
+```rb
+require 'openssl'
+require 'base64'
+
+key = 'webwidget.hmac_token'
+message = 'identifier'
+
+OpenSSL::HMAC.hexdigest('sha256', key, message)
+```
+
+```elixir
+key = 'webwidget.hmac_token'
+message = 'identifier'
+
+signature = :crypto.hmac(:sha256, key, message)
+
+Base.encode16(signature, case: :lower)
+```
+
+
+```go
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/hex"
+)
+
+func main() {
+  secret := []byte("webwidget.hmac_token")
+  message := []byte("identifier")
+
+  hash := hmac.New(sha256.New, secret)
+  hash.Write(message)
+  hex.EncodeToString(hash.Sum(nil))
+}
+```
+
+```py
+import hashlib
+import hmac
+import base64
+
+message = bytes('webwidget.hmac_token', 'utf-8')
+secret = bytes('identifier', 'utf-8')
+
+hash = hmac.new(secret, message, hashlib.sha256)
+hash.hexdigest()
+```