feat: allow injecting an authorization middleware (#6)

Author: billiegoose

README.md

@@ -39,13 +39,73 @@ Kill the process with the PID specified in `$PWD/cors-proxy.pid`:
 cors-proxy stop
 ```
 
-## Configuration
+### CLI configuration
 
 Environment variables:
 - `PORT` the port to listen to (if run with `npm start`)
 - `ALLOW_ORIGIN` the value for the 'Access-Control-Allow-Origin' CORS header
 - `INSECURE_HTTP_ORIGINS` comma separated list of origins for which HTTP should be used instead of HTTPS (added to make developing against locally running git servers easier)
 
+
+## Middleware usage
+
+You can also use the `cors-proxy` as a middleware in your own server.
+
+```js
+const express = require('express')
+const corsProxy = require('@isomorphic-git/cors-proxy/middleware.js')
+
+const app = express()
+const options = {}
+
+app.use(corsProxy(options))
+
+```
+
+### Middleware configuration
+
+*The middleware doesn't use the environment variables.* The options object supports the following properties:
+
+- `origin`: _string_. The value for the 'Access-Control-Allow-Origin' CORS header
+- `insecure_origins`: _string[]_. Array of origins for which HTTP should be used instead of HTTPS (added to make developing against locally running git servers easier)
+- `authorization`: _(req, res, next) => void_. A middleware function you can use to handle custom authorization. Is run after filtering for git-like requests and handling CORS but before the request is proxied.
+
+_Example:_
+```ts
+app.use(
+  corsProxy({
+    authorization: (req: Request, res: Response, next: NextFunction) => {
+      // proxied git HTTP requests already use the Authorization header for git credentials,
+      // so their [Company] credentials are inserted in the X-Authorization header instead.
+      if (getAuthorizedUser(req, 'X-Authorization')) {
+        return next();
+      } else {
+        return res.status(401).send("Unable to authenticate you with [Company]'s git proxy");
+      }
+    },
+  })
+);
+
+// Only requests with a valid JSON Web Token will be proxied
+function getAuthorizedUser(req: Request, header: string = 'Authorization') {
+  const Authorization = req.get(header);
+
+  if (Authorization) {
+    const token = Authorization.replace('Bearer ', '');
+    try {
+      const verifiedToken = verify(token, env.APP_SECRET) as IToken;
+      if (verifiedToken) {
+        return {
+          id: verifiedToken.userId,
+        };
+      }
+    } catch (e) {
+      // noop
+    }
+  }
+}
+```
+
 ## License
 
 This work is released under [The MIT License](https://opensource.org/licenses/MIT)

middleware.js

@@ -19,6 +19,7 @@ const allowHeaders = [
   'range',
   'referer',
   'user-agent',
+  'x-authorization',
   'x-http-method-override',
   'x-requested-with',
 ]
@@ -58,19 +59,47 @@ const filter = (predicate, middleware) => {
   return corsProxyMiddleware
 }
 
-module.exports = ({ origin, insecure_origins = [] } = {}) => {
+const compose = (...handlers) => {
+  const composeTwo = (handler1, handler2) => {
+    function composed (req, res, next) {
+      handler1(req, res, (err) => {
+        if (err) {
+          return next(err)
+        } else {
+          return handler2(req, res, next)
+        }
+      })
+    }
+    return composed
+  }
+  let result = handlers.pop()
+  while(handlers.length) {
+    result = composeTwo(handlers.pop(), result)
+  }
+  return result
+}
+
+function noop (_req, _res, next) {
+  next()
+}
+
+module.exports = ({ origin, insecure_origins = [], authorization = noop } = {}) => {
   function predicate (req) {
     let u = url.parse(req.url, true)
     // Not a git request, skip
     return allow(req, u)
   }
-  function middleware (req, res) {
-    let u = url.parse(req.url, true)
-
+  function sendCorsOK (req, res, next) {
     // Handle CORS preflight request
     if (req.method === 'OPTIONS') {
       return send(res, 200, '')
+    } else {
+      next()
     }
+  }
+  function middleware (req, res) {
+    let u = url.parse(req.url, true)
+
 
     let headers = {}
     for (let h of allowHeaders) {
@@ -110,5 +139,5 @@ module.exports = ({ origin, insecure_origins = [] } = {}) => {
     allowCredentials: false,
     origin
   })
-  return filter(predicate, cors(middleware))
+  return filter(predicate, cors(compose(sendCorsOK, authorization, middleware)))
 }