add new signature example file for node.js

examples/signature.js

@@ -0,0 +1,31 @@
+const crypto = require('crypto')
+
+const KEY = '943b421c9eb07c830af81030552c86009268de4e532ba2ee2eab8247c6da0881'
+const SALT = '520f986b998545b4785e0defbc4f3c1203f22de2374a3d53cb7a7fe9fea309c5'
+
+const urlSafeBase64 = (string) => {
+  return new Buffer(string).toString('base64').replace(/=/g, '').replace(/\+/g, '-').replace(/\//g, '_')
+}
+
+const hexDecode = (hex) => Buffer.from(hex, 'hex')
+
+const sign = (salt, target, secret) => {
+  const hmac = crypto.createHmac('sha256', hexDecode(secret))
+  hmac.update(hexDecode(salt))
+  hmac.update(target)
+  return urlSafeBase64(hmac.digest())
+}
+
+const url = 'http://img.example.com/pretty/image.jpg'
+const resizing_type = 'fill'
+const width = 300
+const height = 300
+const gravity = 'no'
+const enlarge = 1
+const extension = 'png'
+const encoded_url = urlSafeBase64(url)
+const path = `/${resizing_type}/${width}/${height}/${gravity}/${enlarge}/${encoded_url}.${extension}`
+
+const signature = sign(SALT, path, KEY)
+const result = `/${signature}${path}`
+console.log(result)