Allow authenticating with bearer token

README.md

@@ -19,10 +19,10 @@ Main features:
 
 ### Configuration
 
-Whether running manually or via the Docker image, the configuration is set 
+Whether running manually or via the Docker image, the configuration is set
 via environment variables. When running manually, copy `.env.default`
-into `.env`, set the values and they will be loaded automatically. 
-When using the Docker image, set the environment variables when running 
+into `.env`, set the values and they will be loaded automatically.
+When using the Docker image, set the environment variables when running
 the container.
 
 ### Docker
@@ -37,11 +37,20 @@ You will need to configure a webhook receiver in Alertmanager. It should looks s
 receivers:
 - name: 'myreceiver'
   webhook_configs:
-  - url: 'https://my-matrix-alertmanager.tld/alerts?secret=veryverysecretkeyhere'
+  - url: 'https://my-matrix-alertmanager.tld/alerts'
+    http_config:
+      authorization:
+        type: Bearer
+        credentials: 'veryverysecretkeyhere'
 ```
 
 The secret key obviously should match the one in the alertmanager configuration.
 
+The configuration above will pass the secret as an Authorization
+header bearer token, alternatively you can pass it as a query
+parameter `secret`, but if you do it that way then it is not redacted
+from the Alertmanager web UI so this is not really recommended.
+
 ### Prometheus rules
 
 Add some styling to your prometheus rules

src/routes.js

@@ -1,16 +1,39 @@
 const client = require('./client')
 const utils = require('./utils')
 
+const crypto = require('crypto')
+
+const passwordsEqual = (a, b) => {
+    return a && b && a.length === b.length && crypto.timingSafeEqual(Buffer.from(a), Buffer.from(b))
+}
+
 const routes = {
     getRoot: (req, res) => {
         res.send('Hey 👋')
     },
     postAlerts: async (req, res) => {
-        const secret = req.query.secret
-        if (secret !== process.env.APP_ALERTMANAGER_SECRET) {
+        let authorized = false
+        let expectedSecret = process.env.APP_ALERTMANAGER_SECRET
+
+        if (!expectedSecret) {
+            console.error("APP_ALERTMANAGER_SECRET is not configured, unable to authenticate requests")
+            res.status(500).end()
+            return
+        }
+
+        if (passwordsEqual(req.query.secret, expectedSecret)) {
+            authorized = true
+        }
+
+        if (passwordsEqual(req.get('authorization'), `Bearer ${expectedSecret}`)) {
+            authorized = true
+        }
+
+        if (!authorized) {
             res.status(403).end()
             return
         }
+
         const alerts = utils.parseAlerts(req.body)
 
         if (!alerts) {